The following are known Action Replay Codes for Disney/Pixar Monsters, Inc. on Nintendo Game Boy Advance (GBA).
These codes were also known as GameShark Codes and in most cases will work on both devices.

These codes are for the U.S. version of the game.

Master Code – Must Be On
c464ca72
6adde240
11d3e268
78889c91

Infinite Health
8adb517a
a56cccf3

Infinite Lives
051287e7
b91f7966

Infinite Candies
f54dd5a2
66a74ac1

Infinite Laugh Canisters
94c778b3
52cf97ef