The following are known Action Replay Codes for Mobile Suit Gundam Seed: Battle Assault 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
c92eb82f
bda01bef
0c7d07c8
c78400f7

Infinite OS Points
f1f70071
aff788c7
4c77ba3f
ca4edcb6

Player 1: Infinite Health
9ac5ebd9
954554e0
0ddcb99c
f04e2dc0

Player 1: Infinite Armor
9ac5ebd9
954554e0
96519a2c
b6188c39

Player 1: Infinite Thrust
9ac5ebd9
954554e0
d8b60bf1
4d5d7906

Player 2: No Health
4282da78
49a69679
3bb48218
8504d002

Player 2: No Armor
3241eb70
4f684057
9aa95965
879c099a

Player 2: No Thrust
88f05ee1
5c471f9a
8be136a0
f0a73582