World 1 is the first world in New Super Mario Bros. Wii, containing six levels, a fortress, a castle, and a boss, three special stages - accessible by entering the Mushroom Houses - as well as housing Princess Peach's Castle. There are three special stages, two Red Toad Houses, and one Gold Toad House; the two Red Toad Houses occurring upon completion of World's 1-2 and 1-4, and the Gold Mushroom House occurring upon the completion of World 1-3.
Note: italics are secret exits.
|1-1||World 1-2||The first level of New Super Mario Bros. Wii. It introduces the Propeller Suit, Goombas and Koopa Troopas. This level is designed for new players.|
|1-2||World 1-3, Red Mushroom House||This is the first underground level. This is also the first level with the Ice Flower power-up.|
|1-3||World 1-Fortress, Gold Mushroom House, 1-Cannon||This level is the first level to feature Yoshi and has another secret exit, which is found by moving to the top of the fields and enter through the pipe.|
|1-Cannon||World 5-1||N/A||The Warp Cannon of World 1, leading directly to World 5. It is unlocked by finding the secret exit of the above level.|
|1-Tower||World 1-4||This is a tower level, featuring swinging platforms and moving stone blocks. Larry Koopa is the boss here.|
|1-4||Enemy Area, World 1-5, World 1-6, Red Mushroom House||This is an underwater level, featuring Cheep Cheeps.|
|1-5||World 1-Castle||This is the first athletic level of New Super Mario Bros. Wii, containing regular and screw-controlled mushrooms, as well as spinning blocks.|
|1-6||World 1-Castle||A grassland level containing many rolling hills. Koopa Troopas and Koopa Paratroopas are the main enemies.|
|1-Castle||World 2-1, World 2-2||The first castle level of New Super Mario Bros. Wii. It contains lava pools, Thwomps, and giant spinning gears. Larry Koopa is the boss here again.|