diff --git a/.changeset/cold-dolls-applaud.md b/.changeset/cold-dolls-applaud.md
new file mode 100644
index 00000000000..3af11fa80c7
--- /dev/null
+++ b/.changeset/cold-dolls-applaud.md
@@ -0,0 +1,5 @@
+---
+"@smithy/config-resolver": minor
+---
+
+validate region is hostname component
diff --git a/packages/config-resolver/package.json b/packages/config-resolver/package.json
index cdad938d9f9..7c6eadc1aa7 100644
--- a/packages/config-resolver/package.json
+++ b/packages/config-resolver/package.json
@@ -28,6 +28,7 @@
     "@smithy/node-config-provider": "workspace:^",
     "@smithy/types": "workspace:^",
     "@smithy/util-config-provider": "workspace:^",
+    "@smithy/util-endpoints": "workspace:^",
     "@smithy/util-middleware": "workspace:^",
     "tslib": "^2.6.2"
   },
diff --git a/packages/config-resolver/src/regionConfig/checkRegion.spec.ts b/packages/config-resolver/src/regionConfig/checkRegion.spec.ts
new file mode 100644
index 00000000000..9781ad5fb9c
--- /dev/null
+++ b/packages/config-resolver/src/regionConfig/checkRegion.spec.ts
@@ -0,0 +1,77 @@
+import { isValidHostLabel } from "@smithy/util-endpoints";
+import { describe, expect, test as it, vi } from "vitest";
+
+import { checkRegion } from "./checkRegion";
+
+describe("checkRegion", () => {
+  const acceptedRegionExamples = [
+    "us-east-1",
+    "ap-east-1",
+    "ap-southeast-4",
+    "ap-northeast-3",
+    "ap-northeast-1",
+    "eu-west-2",
+    "il-central-1",
+    "mx-central-1",
+    "eu-isoe-santaclaus-125",
+    "us-iso-reindeer-3000",
+    "eusc-de-gingerbread-8000",
+    "abcd",
+    "12345",
+  ];
+
+  it("does not throw when the region is a valid host label", () => {
+    for (const region of acceptedRegionExamples) {
+      expect(() => checkRegion(region)).not.toThrow();
+    }
+  });
+
+  it("throws when the region is not a valid host label", () => {
+    for (const region of [
+      "us-east-1-",
+      "a".repeat(64),
+      "-us-east-1",
+      "",
+      "!",
+      "@",
+      "#",
+      "$",
+      "%",
+      "^",
+      "&",
+      "*",
+      "(",
+      ")",
+      ".",
+      "[",
+      "]",
+      ";",
+      `'`,
+      "?",
+      "/",
+      "\\",
+      "|",
+      "+-*/",
+    ]) {
+      expect(() => checkRegion(region)).toThrow(
+        `Region not accepted: region="${region}" is not a valid hostname component.`
+      );
+    }
+  });
+
+  it("caches accepted regions", () => {
+    const di = {
+      isValidHostLabel,
+    };
+    for (const region of acceptedRegionExamples) {
+      expect(() => checkRegion(region, di.isValidHostLabel)).not.toThrow();
+    }
+    vi.spyOn(di, "isValidHostLabel").mockImplementation(isValidHostLabel);
+    for (const region of acceptedRegionExamples) {
+      expect(() => checkRegion(region, di.isValidHostLabel)).not.toThrow();
+    }
+    expect(di.isValidHostLabel).toHaveBeenCalledTimes(0);
+    expect(() => checkRegion("oh-canada", di.isValidHostLabel)).not.toThrow();
+    expect(di.isValidHostLabel).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/packages/config-resolver/src/regionConfig/checkRegion.ts b/packages/config-resolver/src/regionConfig/checkRegion.ts
new file mode 100644
index 00000000000..c8f754270e1
--- /dev/null
+++ b/packages/config-resolver/src/regionConfig/checkRegion.ts
@@ -0,0 +1,22 @@
+import { isValidHostLabel } from "@smithy/util-endpoints";
+
+/**
+ * @internal
+ */
+const validRegions = new Set<string>();
+
+/**
+ * Checks whether region can be a host component.
+ *
+ * @param region - to check.
+ * @param check - checking function.
+ *
+ * @internal
+ */
+export const checkRegion = (region: string, check = isValidHostLabel) => {
+  if (!validRegions.has(region) && !check(region)) {
+    throw new Error(`Region not accepted: region="${region}" is not a valid hostname component.`);
+  } else {
+    validRegions.add(region);
+  }
+};
diff --git a/packages/config-resolver/src/regionConfig/resolveRegionConfig.ts b/packages/config-resolver/src/regionConfig/resolveRegionConfig.ts
index 894287fe957..af8ed63e364 100644
--- a/packages/config-resolver/src/regionConfig/resolveRegionConfig.ts
+++ b/packages/config-resolver/src/regionConfig/resolveRegionConfig.ts
@@ -1,5 +1,6 @@
 import type { Provider } from "@smithy/types";
 
+import { checkRegion } from "./checkRegion";
 import { getRealRegion } from "./getRealRegion";
 import { isFipsRegion } from "./isFipsRegion";
 
@@ -47,11 +48,10 @@ export const resolveRegionConfig = <T>(input: T & RegionInputConfig & Previously
 
   return Object.assign(input, {
     region: async () => {
-      if (typeof region === "string") {
-        return getRealRegion(region);
-      }
-      const providedRegion = await region();
-      return getRealRegion(providedRegion);
+      const providedRegion = typeof region === "function" ? await region() : region;
+      const realRegion = getRealRegion(providedRegion);
+      checkRegion(realRegion);
+      return realRegion;
     },
     useFipsEndpoint: async () => {
       const providedRegion = typeof region === "string" ? region : await region();
diff --git a/packages/util-endpoints/src/lib/isValidHostLabel.spec.ts b/packages/util-endpoints/src/lib/isValidHostLabel.spec.ts
index 2a0663e3bcf..396924cc7e4 100644
--- a/packages/util-endpoints/src/lib/isValidHostLabel.spec.ts
+++ b/packages/util-endpoints/src/lib/isValidHostLabel.spec.ts
@@ -32,7 +32,7 @@ describe(isValidHostLabel.name, () => {
       expect(isValidHostLabel(hostLabelToTest, true)).toBe(output);
     });
 
-    describe("returns false is any subdomain is invalid", () => {
+    describe("returns false if any subdomain is invalid", () => {
       const validHostLabel = testCases
         .filter(([outputEntry]) => outputEntry === true)
         .map(([, value]) => value)
diff --git a/yarn.lock b/yarn.lock
index 44de7676aab..d6941dc3027 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2514,6 +2514,7 @@ __metadata:
     "@smithy/node-config-provider": "workspace:^"
     "@smithy/types": "workspace:^"
     "@smithy/util-config-provider": "workspace:^"
+    "@smithy/util-endpoints": "workspace:^"
     "@smithy/util-middleware": "workspace:^"
     concurrently: "npm:7.0.0"
     downlevel-dts: "npm:0.10.1"