The following are known Action Replay Codes for Classic NES Series: Super Mario Bros. 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
f27f40d9
9d9a7538
f23b723c
1647b6e0

Infinite Lives
b9b2b3e6
1641e354

Always Little Mario
052f97ee
b47ccca6

Always Big Mario
2d1341a0
de954ef4

Always Fire Mario
f2a983a9
fffc61e7

Invincible
1e00b936
0bc46a93

Infinite Time
58902e29
160ada21

Enable Hard Mode
3d683721
b452b79a