Vowel World is a world in Mario's Early Years! Fun with Letters. It is one of the seven islands in the game and is represented by an island with the letters A E I O U above.
This world takes place underwater. Like all the levels in the game, Mario goes through pipes to go to the next level. Each level looks the same, with some seaweed in the background and coral.
For this location, the player learns how to identify words that start with the vowels A E I O U. There are four words, three of which start with the vowel indicated on-screen. The player must click these three words to continue. There are five levels for each vowel A, E, I, O and U.