Super Monkey Ball Jr. is a port of the original Super Monkey Ball designed for the Game Boy Advance. The game was developed by THQ and Realism with the supervision of Amusement Vision, and was published by Sega. This is the first handheld Super Monkey Ball game in the series.
The Main Game is similar to Super Monkey Ball's, but with less floors due to hardware limitations. Most of the 74 available floors are direct ports form Super Monkey Ball while others are new. The levels are spread across four difficulties. Beginner has 10 floors, Advanced has 20 floors, Expert has 30 floors, and Master has 5 floors. Each set of levels except for Master also includes three Extra Floors if the player completes the difficulties without using a continue.
The gameplay is identical to its console counterpart, where players control the stage with the D-Pad (with the A and B buttons increasing and decreasing the stage's tilt respectively) to guide their monkey to the goal while collecting bananas to earn points and get extra lives. One scoring type added to Jr. is the "Perfect" bonus, which applies an extra 2x multiplayer to the score for that floor if all the Bananas in a level are collected before touching the Goal.
- Sky High (Uses Monkey Mall's theme)
- Storm (Uses Sky High's theme)
- Lava Land (Uses Storm's theme)
The Mini Games in Jr. are based on the party games from Super Monkey Ball. However, Monkey Duel is exclusive to Super Monkey Ball Jr. Each game apart from Duel are purchased for 2500 Play Points, with Monkey Golf containing a second course that must be bought separately.
Both Monkey Duel and Monkey Fight require multiple Game Boy Advances and multiple copies of Super Monkey Ball Jr. to play in multiplayer, along with the necessary number of Link Cables. Monkey Bowling and Monkey Golf, on the other hand, can additionally be played using one Game Boy Advance, as players alternate between turns.
- This game is considered more difficult than other games in the series due to the lack of an analog stick, instead using the D-pad for movement and the A and B buttons for controlling the player's speed. This locks control to eight directions.
- Upon entering the Konami Code at the title screen, it will read "Super Nice Try" instead of "Super Monkey Ball Jr.".
- Easily unlock everything by entering Down, Down, Up, Up, Left, Right, Left, Right, B, A on the Title Screen. You know it worked if the game saves then the Title Screen reads "Super Enable All" instead of "Super Monkey Ball Jr."
- Make the game look blocky by entering Left, Left, Right, Right, Down, Down, A. This effect persists until the game is reset. You know it worked if the Title Screen reads "Super Blocky Mode" instead of "Super Monkey Ball Jr."
- If a banana is collected while reaching the goal, and that banana results in obtaining a 1up, the game will prioritize showing the "1up" message instead of showing "Goal" as normal.