The following are known Action Replay Codes for Boxing Fever 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
fa7ece5e
20ee406b
b39a86a9
a647f523

Infinite Health
e4efdf7c
dcda64eb

Infinite Stamina
55aec3c5
3a47fbdb

1 Hit Knock-Outs
f7a31434
6b39f2e6
258f27b3
07465f14

Always Round 1
eedc65cc
430cba1c

Play as Boxor
9a3787c2
9a09117a
4945ddd3
f3816d59
76624e94
cd7d1841
7ed0e6d2
34efb242
fc1e4797
f2f804a1
62f5f218
c980218f

Play as Byclops
df5e5870
7e7727c1
3604ec67
b030496c
84ebbfea
cd6f1e52
2fe68b5c
0d773b9f
52f640eb
3c8f14df
9ef4710a
2c860376