diff --git a/modules/rostests/apitests/ntdll/CMakeLists.txt b/modules/rostests/apitests/ntdll/CMakeLists.txt
index 71f8ec4af7e..223d7d5276f 100644
--- a/modules/rostests/apitests/ntdll/CMakeLists.txt
+++ b/modules/rostests/apitests/ntdll/CMakeLists.txt
@@ -129,6 +129,8 @@ list(APPEND SOURCE
     RtlNtPathNameToDosPathName.c
     RtlpApplyLengthFunction.c
     RtlpEnsureBufferSize.c
+    RtlQueryEnvironmentVariable.c
+    RtlQueryEnvironmentVariable_U.c
     RtlQueryTimeZoneInfo.c
     RtlReAllocateHeap.c
     RtlRemovePrivileges.c
diff --git a/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable.c b/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable.c
new file mode 100644
index 00000000000..2d34d4d5777
--- /dev/null
+++ b/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable.c
@@ -0,0 +1,98 @@
+/*
+ * PROJECT:     ReactOS API tests
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Tests for RtlQueryEnvironmentVariable
+ * COPYRIGHT:   Copyright 2026 Timo Kreuzer <timo.kreuzer@reactos.org>
+ */
+
+#include "precomp.h"
+
+typedef
+NTSTATUS
+NTAPI
+FN_RtlQueryEnvironmentVariable(
+    _In_opt_ PVOID Environment,
+    _In_reads_(NameLength) PWSTR Name,
+    _In_ SIZE_T NameLength,
+    _Out_writes_(ValueLength) PWSTR Value,
+    _In_ SIZE_T ValueLength,
+    _Out_ PSIZE_T ReturnLength);
+
+static FN_RtlQueryEnvironmentVariable* pRtlQueryEnvironmentVariable;
+
+START_TEST(RtlQueryEnvironmentVariable)
+{
+    static WCHAR TestEnv[] = L"TestVar=TestVal\0Foo=4\0EmptyVar\0Bar=8\0\0";
+    WCHAR Buffer[32];
+    SIZE_T ReturnLength;
+    NTSTATUS Status;
+
+    HINSTANCE hinst = GetModuleHandleA("ntdll.dll");
+    pRtlQueryEnvironmentVariable = (FN_RtlQueryEnvironmentVariable*)
+        GetProcAddress(hinst, "RtlQueryEnvironmentVariable");
+    if (pRtlQueryEnvironmentVariable == NULL)
+    {
+        ok(GetNTVersion() < _WIN32_WINNT_VISTA, "RtlQueryEnvironmentVariable not available on NT6+\n");
+        skip("RtlQueryEnvironmentVariable is not available\n");
+        return;
+    }
+
+    /* Query the TestVar environment variable length */
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 7, NULL, 0, &ReturnLength);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_size(ReturnLength, 8);
+
+    /* Test a buffer size that is too small */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 7, Buffer, 2, &ReturnLength);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_size(ReturnLength, 8);
+    ok_eq_wchar(Buffer[0], UNICODE_NULL);
+    ok_eq_wchar(Buffer[1], 0xABAB);
+
+    /* Test a buffer size that doesn't fit the terminating NULL char */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 7, Buffer, 7, &ReturnLength);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_size(ReturnLength, 8);
+    ok_eq_wchar(Buffer[0], UNICODE_NULL);
+    ok_eq_wchar(Buffer[1], 0xABAB);
+
+    /* Test a buffer size that is just large enough */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 7, Buffer, 8, &ReturnLength);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_size(ReturnLength, 7);
+    ok_eq_wstr(Buffer, L"TestVal");
+    ok_eq_wchar(Buffer[7], UNICODE_NULL);
+    ok_eq_wchar(Buffer[8], 0xABAB);
+
+    /* Test a buffer size that is larger than needed */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 7, Buffer, ARRAYSIZE(Buffer), &ReturnLength);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_size(ReturnLength, 7);
+    ok_eq_wstr(Buffer, L"TestVal");
+    ok_eq_wchar(Buffer[7], UNICODE_NULL);
+    ok_eq_wchar(Buffer[8], 0xABAB);
+
+    /* Test a too big variable Length */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"TestVar", 8, Buffer, 8, &ReturnLength);
+    ok_ntstatus(Status, STATUS_VARIABLE_NOT_FOUND);
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+    /* Query the EmptyVar environment variable */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"EmptyVar", 8, Buffer, ARRAYSIZE(Buffer), &ReturnLength);
+    ok_ntstatus(Status, STATUS_VARIABLE_NOT_FOUND);
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+    /* Query the Bar environment variable */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    Status = pRtlQueryEnvironmentVariable(TestEnv, L"Bar", 3, Buffer, 8, &ReturnLength);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_wchar(Buffer[0], L'8');
+    ok_eq_wchar(Buffer[1], UNICODE_NULL);
+    ok_eq_wchar(Buffer[2], 0xABAB);
+}
diff --git a/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable_U.c b/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable_U.c
new file mode 100644
index 00000000000..974556ef3c9
--- /dev/null
+++ b/modules/rostests/apitests/ntdll/RtlQueryEnvironmentVariable_U.c
@@ -0,0 +1,128 @@
+/*
+ * PROJECT:     ReactOS API tests
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Tests for RtlQueryEnvironmentVariable_U
+ * COPYRIGHT:   Copyright 2026 Timo Kreuzer <timo.kreuzer@reactos.org>
+ */
+
+#include "precomp.h"
+
+START_TEST(RtlQueryEnvironmentVariable_U)
+{
+    static WCHAR TestEnvironment[] = L"TestVar=TestVal\0Foo=4\0EmptyVar\0Bar=8\0\0";
+    WCHAR Buffer[32];
+    UNICODE_STRING NameString, ValueString;
+    NTSTATUS Status;
+
+    /* Query the TestVar environment variable length */
+    RtlInitUnicodeString(&NameString, L"TestVar");
+    RtlInitEmptyUnicodeString(&ValueString, NULL, 0);
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_pointer(ValueString.Buffer, NULL);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, 0);
+
+    /* Test passing an empty sized buffer */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, 0);
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, 0);
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+    /* Test a buffer size that is too small */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, 2 * sizeof(WCHAR));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_BUFFER_TOO_SMALL);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, 2 * sizeof(WCHAR));
+    ok(Buffer[0] == UNICODE_NULL || broken(/* Windows 2003 */ Buffer[0] == 0xABAB), "Buffer[0] = 0x%x\n", Buffer[0]);
+    ok_eq_wchar(Buffer[1], 0xABAB);
+
+    /* Test a buffer size that doesn't fit the terminating NULL char */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, 7 * sizeof(WCHAR));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok(Status == STATUS_BUFFER_TOO_SMALL || broken(/* Windows 2003 */ Status == STATUS_SUCCESS), "Status = 0x%lx\n", Status);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, 7 * sizeof(WCHAR));
+    if (Status == STATUS_BUFFER_TOO_SMALL)
+    {
+        ok_eq_wchar(Buffer[0], UNICODE_NULL);
+        ok_eq_wchar(Buffer[1], 0xABAB);
+    }
+
+    /* Test a buffer size that is just large enough */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, 8 * sizeof(WCHAR));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, 8 * sizeof(WCHAR));
+    ok_eq_wstr(Buffer, L"TestVal");
+    ok_eq_wchar(Buffer[7], UNICODE_NULL);
+    ok_eq_wchar(Buffer[8], 0xABAB);
+
+    /* Test a buffer size that is larger than needed */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, sizeof(Buffer));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 7 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, sizeof(Buffer));
+    ok_eq_wstr(Buffer, L"TestVal");
+    ok_eq_wchar(Buffer[7], UNICODE_NULL);
+    ok_eq_wchar(Buffer[8], 0xABAB);
+
+    /* Test a too big variable Length */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    NameString.Length += sizeof(WCHAR);
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, sizeof(Buffer));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_VARIABLE_NOT_FOUND);
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+    /* Query the EmptyVar environment variable */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitUnicodeString(&NameString, L"EmptyVar");
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, sizeof(Buffer));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_VARIABLE_NOT_FOUND);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 0);
+    ok_eq_ulong(ValueString.MaximumLength, sizeof(Buffer));
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+    /* Query the Bar environment variable */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitUnicodeString(&NameString, L"Bar");
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, sizeof(Buffer));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_SUCCESS);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 1 * sizeof(WCHAR));
+    ok_eq_ulong(ValueString.MaximumLength, sizeof(Buffer));
+    ok_eq_wstr(Buffer, L"8");
+    ok_eq_wchar(Buffer[1], UNICODE_NULL);
+    ok_eq_wchar(Buffer[2], 0xABAB);
+
+    /* Test NULL Variable name */
+    memset(Buffer, 0xAB, sizeof(Buffer));
+    RtlInitEmptyUnicodeString(&NameString, NULL, 0);
+    RtlInitEmptyUnicodeString(&ValueString, Buffer, sizeof(Buffer));
+    Status = RtlQueryEnvironmentVariable_U(TestEnvironment, &NameString, &ValueString);
+    ok_ntstatus(Status, STATUS_VARIABLE_NOT_FOUND);
+    ok_eq_pointer(ValueString.Buffer, Buffer);
+    ok_eq_ulong(ValueString.Length, 0);
+    ok_eq_ulong(ValueString.MaximumLength, sizeof(Buffer));
+    ok_eq_wchar(Buffer[0], 0xABAB);
+
+}
diff --git a/modules/rostests/apitests/ntdll/testlist.c b/modules/rostests/apitests/ntdll/testlist.c
index 6584eaf0f9b..c404ac2aa27 100644
--- a/modules/rostests/apitests/ntdll/testlist.c
+++ b/modules/rostests/apitests/ntdll/testlist.c
@@ -117,6 +117,8 @@ extern void func_RtlMultipleAllocateHeap(void);
 extern void func_RtlNtPathNameToDosPathName(void);
 extern void func_RtlpApplyLengthFunction(void);
 extern void func_RtlpEnsureBufferSize(void);
+extern void func_RtlQueryEnvironmentVariable(void);
+extern void func_RtlQueryEnvironmentVariable_U(void);
 extern void func_RtlQueryTimeZoneInformation(void);
 extern void func_RtlReAllocateHeap(void);
 extern void func_RtlRemovePrivileges(void);
@@ -250,6 +252,8 @@ const struct test winetest_testlist[] =
     { "RtlNtPathNameToDosPathName",     func_RtlNtPathNameToDosPathName },
     { "RtlpApplyLengthFunction",        func_RtlpApplyLengthFunction },
     { "RtlpEnsureBufferSize",           func_RtlpEnsureBufferSize },
+    { "RtlQueryEnvironmentVariable",    func_RtlQueryEnvironmentVariable },
+    { "RtlQueryEnvironmentVariable_U",  func_RtlQueryEnvironmentVariable_U },
     { "RtlQueryTimeZoneInformation",    func_RtlQueryTimeZoneInformation },
     { "RtlReAllocateHeap",              func_RtlReAllocateHeap },
     { "RtlRemovePrivileges",            func_RtlRemovePrivileges },