diff --git a/packages/auth/src/Auth.ts b/packages/auth/src/Auth.ts
index 8fc1b9c7ca8..f5bfdeee26b 100644
--- a/packages/auth/src/Auth.ts
+++ b/packages/auth/src/Auth.ts
@@ -43,6 +43,7 @@ import {
 	Parser,
 	JS,
 	UniversalStorage,
+	urlSafeDecode,
 } from '@aws-amplify/core';
 import {
 	CookieStorage,
@@ -1974,7 +1975,7 @@ export class AuthClass {
 
 						dispatchAuthEvent(
 							'customOAuthState',
-							customState,
+							urlSafeDecode(customState),
 							`State for user ${currentUser.getUsername()}`
 						);
 					}
diff --git a/packages/auth/src/OAuth/OAuth.ts b/packages/auth/src/OAuth/OAuth.ts
index 7b61bd0417e..31428f06746 100644
--- a/packages/auth/src/OAuth/OAuth.ts
+++ b/packages/auth/src/OAuth/OAuth.ts
@@ -21,7 +21,7 @@ import {
 	CognitoHostedUIIdentityProvider,
 } from '../types/Auth';
 
-import { ConsoleLogger as Logger, Hub } from '@aws-amplify/core';
+import { ConsoleLogger as Logger, Hub, urlSafeEncode } from '@aws-amplify/core';
 
 import sha256 from 'crypto-js/sha256';
 import Base64 from 'crypto-js/enc-base64';
@@ -78,11 +78,18 @@ export default class OAuth {
 		customState?: string
 	) {
 		const generatedState = this._generateState(32);
+
+		/* encodeURIComponent is not URL safe, use urlSafeEncode instead. Cognito 
+		single-encodes/decodes url on first sign in and double-encodes/decodes url
+		when user already signed in. Using encodeURIComponent, Base32, Base64 add 
+		characters % or = which on further encoding becomes unsafe. '=' create issue 
+		for parsing query params. 
+		Refer: https://github.com/aws-amplify/amplify-js/issues/5218 */
 		const state = customState
-			? `${generatedState}-${customState}`
+			? `${generatedState}-${urlSafeEncode(customState)}`
 			: generatedState;
 
-		oAuthStorage.setState(encodeURIComponent(state));
+		oAuthStorage.setState(state);
 
 		const pkce_key = this._generateRandom(128);
 		oAuthStorage.setPKCE(pkce_key);
diff --git a/packages/core/__tests__/StringUtils-test.ts b/packages/core/__tests__/StringUtils-test.ts
new file mode 100644
index 00000000000..aecf7838f2f
--- /dev/null
+++ b/packages/core/__tests__/StringUtils-test.ts
@@ -0,0 +1,27 @@
+import { urlSafeEncode, urlSafeDecode } from '../src/Util';
+import { TextDecoder, TextEncoder } from 'util';
+global.TextEncoder = TextEncoder;
+global.TextDecoder = TextDecoder;
+
+const complexCustomState = 'https://amplify-app:300/?empty=&list=1,a,%,@';
+
+describe('StringUtils', () => {
+	test('urlSafe encoding', () => {
+		const urlSafeState = urlSafeEncode(complexCustomState);
+		expect(encodeURIComponent(urlSafeState)).toEqual(urlSafeState);
+	});
+	test('urlSafe decoding', () => {
+		const urlSafeState = urlSafeEncode(complexCustomState);
+		const encodedState = encodeURIComponent(urlSafeState);
+
+		expect(decodeURIComponent(encodedState)).toEqual(encodedState);
+	});
+	test('URI encode/decode with url safe state', () => {
+		const urlSafeState = urlSafeEncode(complexCustomState);
+		const encodedState = encodeURIComponent(urlSafeState);
+
+		expect(urlSafeDecode(decodeURIComponent(encodedState))).toEqual(
+			complexCustomState
+		);
+	});
+});
diff --git a/packages/core/src/Util/StringUtils.ts b/packages/core/src/Util/StringUtils.ts
new file mode 100644
index 00000000000..53e19c0f3a1
--- /dev/null
+++ b/packages/core/src/Util/StringUtils.ts
@@ -0,0 +1,18 @@
+export function urlSafeEncode(str: string) {
+	return str
+		.split('')
+		.map(char =>
+			char
+				.charCodeAt(0)
+				.toString(16)
+				.padStart(2, '0')
+		)
+		.join('');
+}
+
+export function urlSafeDecode(hex: string) {
+	return hex
+		.match(/.{2}/g)
+		.map(char => String.fromCharCode(parseInt(char, 16)))
+		.join('');
+}
diff --git a/packages/core/src/Util/index.ts b/packages/core/src/Util/index.ts
index e22e2984509..eb130b3dfb4 100644
--- a/packages/core/src/Util/index.ts
+++ b/packages/core/src/Util/index.ts
@@ -2,3 +2,4 @@ export * from './Retry';
 export { default as Mutex } from './Mutex';
 export { default as Reachability } from './Reachability';
 export * from './DateUtils';
+export * from './StringUtils';