The following are known Action Replay Codes for All Star Tennis 99 on Nintendo 64 (N64).

Device Compatibility: Action Replay & GameShark

P2 – One set to win game
301BAEB2 0006

P1 – Can not win any sets
301BAEB1 0000

P2 – Can not win any sets
301BAEB2 0000

P1 – One set to win game
301BAEB1 0006