diff --git a/.gitignore b/.gitignore
index e47c70b..9fd42ff 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,5 @@ dist
 *.njsproj
 *.sln
 *.sw?
+
+vitest-report.xml
diff --git a/package/stringUtil/escapeHtml/index.test.ts b/package/stringUtil/escapeHtml/index.test.ts
index 9fec021..787bc38 100644
--- a/package/stringUtil/escapeHtml/index.test.ts
+++ b/package/stringUtil/escapeHtml/index.test.ts
@@ -1,8 +1,37 @@
-import { expect, test } from "vitest";
+import { describe, expect, test } from "vitest";
 import escapeHtml from ".";
 
-test("HTML 특수 문자를 이스케이프한다.", () => {
-  const input = "<span> 안녕하세요 </span>";
-  const output = escapeHtml(input);
-  expect(output).toBe("&lt;span&gt; 안녕하세요 &lt;/span&gt;");
+describe("escapeHtml 유틸 함수 테스트", () => {
+  test("HTML 특수 문자를 올바르게 이스케이프한다", () => {
+    const input = "<span> 안녕하세요 </span>";
+    const output = escapeHtml(input);
+    expect(output).toBe("&lt;span&gt; 안녕하세요 &lt;/span&gt;");
+  });
+
+  test("여러 HTML 특수 문자를 포함한 문자열을 올바르게 이스케이프한다", () => {
+    const input = "Tom & Jerry <3 \"Best Friends\" 'Forever' / Fun";
+    const output = escapeHtml(input);
+    expect(output).toBe(
+      "Tom &amp; Jerry &lt;3 &quot;Best Friends&quot; &#39;Forever&#39; / Fun"
+    );
+  });
+
+  test("HTML 특수 문자가 없는 문자열은 그대로 반환한다", () => {
+    const input = "Hello World!";
+    const output = escapeHtml(input);
+    expect(output).toBe("Hello World!");
+  });
+
+  test("빈 문자열을 입력하면 빈 문자열을 반환한다", () => {
+    const input = "";
+    const output = escapeHtml(input);
+    expect(output).toBe("");
+  });
+
+  test("null 또는 undefined를 입력하면 그대로 반환한다", () => {
+    // @ts-ignore
+    expect(escapeHtml(null)).toBe(null);
+    // @ts-ignore
+    expect(escapeHtml(undefined)).toBe(undefined);
+  });
 });
diff --git a/package/stringUtil/escapeHtml/index.ts b/package/stringUtil/escapeHtml/index.ts
index 2c43151..9fc1d7b 100644
--- a/package/stringUtil/escapeHtml/index.ts
+++ b/package/stringUtil/escapeHtml/index.ts
@@ -1,4 +1,5 @@
-export default function escapeHtml(str: string): string {
+export default function escapeHtml(str: string | null | undefined): string | null | undefined {
+  if (str == null) return str;
   return str
     .replace(/&/g, "&amp;")
     .replace(/</g, "&lt;")
diff --git a/package/stringUtil/unescapeHtml/index.test.ts b/package/stringUtil/unescapeHtml/index.test.ts
index fcf7d04..54fdc59 100644
--- a/package/stringUtil/unescapeHtml/index.test.ts
+++ b/package/stringUtil/unescapeHtml/index.test.ts
@@ -1,4 +1,4 @@
-import { expect, test } from "vitest";
+import { describe, expect, test } from "vitest";
 import unescapeHtml from ".";
 
 test("HTML 특수 문자를 언이스케이프한다.", () => {
@@ -6,3 +6,31 @@ test("HTML 특수 문자를 언이스케이프한다.", () => {
   const output = unescapeHtml(input);
   expect(output).toBe("<span> 안녕하세요 </span>");
 });
+
+describe("unescapeHtml 유틸 함수 테스트", () => {
+  test("여러 HTML 특수 문자를 포함한 문자열을 올바르게 언이스케이프한다", () => {
+    const input =
+      "Tom &amp; Jerry &lt;3 &quot;Best Friends&quot; &#39;Forever&#39; &#x2F; Fun";
+    const output = unescapeHtml(input);
+    expect(output).toBe("Tom & Jerry <3 \"Best Friends\" 'Forever' / Fun");
+  });
+
+  test("HTML 특수 문자가 없는 문자열은 그대로 반환한다", () => {
+    const input = "Hello World!";
+    const output = unescapeHtml(input);
+    expect(output).toBe("Hello World!");
+  });
+
+  test("빈 문자열을 입력하면 빈 문자열을 반환한다", () => {
+    const input = "";
+    const output = unescapeHtml(input);
+    expect(output).toBe("");
+  });
+
+  test("null 또는 undefined를 입력하면 그대로 반환한다", () => {
+    // @ts-ignore
+    expect(unescapeHtml(null)).toBe(null);
+    // @ts-ignore
+    expect(unescapeHtml(undefined)).toBe(undefined);
+  });
+});
diff --git a/package/stringUtil/unescapeHtml/index.ts b/package/stringUtil/unescapeHtml/index.ts
index 1d85ac6..d126b7d 100644
--- a/package/stringUtil/unescapeHtml/index.ts
+++ b/package/stringUtil/unescapeHtml/index.ts
@@ -1,8 +1,10 @@
-export default function unescapeHtml(str: string): string {
-    return str.replace(/&amp;/g, "&")
-        .replace(/&lt;/g, "<")
-        .replace(/&gt;/g, ">")
-        .replace(/&quot;/g, "\"")
-        .replace(/&#39;/g, "'")
-        .replace(/&#x2F;/g, "/");
-}
\ No newline at end of file
+export default function unescapeHtml(str: string | null | undefined): string | null | undefined {
+  if (str == null) return str;
+  return str
+    .replace(/&amp;/g, "&")
+    .replace(/&lt;/g, "<")
+    .replace(/&gt;/g, ">")
+    .replace(/&quot;/g, '"')
+    .replace(/&#39;/g, "'")
+    .replace(/&#x2F;/g, "/");
+}