The Baseball Kingdom is a small man-made island off the coast of the Mushroom Kingdom. Princess Peach built it so her citizens could all play baseball. It was invaded by King Bowser and his son during the events of Mario Super Sluggers but was ultimately saved by Mario and his baseball team.
The Baseball Kingdom consists of eleven stadiums, each suited to a different player.
- Mario Stadium - The most basic stadium on the coast of the Kingdom. There are no obstacles on it, making it excellent for practice.
- Yoshi Park - A small field surrounded by a theme park. Warp Pipes and a train fight against players.
- Wario City - A concrete field with Wario's Casino in the background. One-way roads and Exploding Manholes serve as obstacles.
- DK Jungle - A wild Jungle surrounded by ruins. Rolling barrels and poisonous flowers secure a hard time fielding
- Peach Ice Gardens - An Opera House with an Ice Rink as the field. Freezies and slippery floors hinder the players
- Bowser Jr's Playroom - A colorful castle of building blocks. Chain Chomps and Bullet Bills attack from nowhere.
- Toy Field - An inclosed arcade space. Used only in a minigame mode. Unlocked in Story mode after receiving a pass
- Luigi's Mansion - An eerie mansion lurks in the background of this graveyard field. Tombstones, fog and ghosts slow down the players. Unlocked after Luigi's Flashlight is bought.
- Daisy Cruiser - The deck of an ocean liner. Gooper Blooper and deck chairs cause trouble. Unlocked after clearing story mode in Peach Ice Gardens.
- Bowser's Castle - A horrifying palace lined with lava. King Bob-omb attacks by dropping bombs as Bowser heads shoot out fireballs. Unlocked after Bowser Jr. has been beaten in Story Mode.