Mario Party 9 (Japanese: マリオパーティ9, Hepburn: Mario Pāti Nain) is a party video game published by Nintendo for the Wii.[3] The ninth main installment in the Mario Party series, it was announced at E3 2011 and released in Europe, North America, and Australia in March 2012, followed by Japan a month later. It was the first game in the series to be developed by NDcube, who took over development of the series from Hudson Soft, which was acquired and dissolved by Konami by March 2012. This was also the final Mario game to be published for the Wii.

Mario Party 9 was the second and last game in the series released for the Wii, and was followed by Mario Party: Island Tour for the Nintendo 3DS in 2013 and Mario Party 10 for the Wii U in 2015.

The game received mixed to positive reviews from critics for its graphics, multiplayer, minigames, content and its overhaul of mechanics, considering it an improvement to its predecessor, however, its car mechanic, linear boards and emphasis on luck were criticized.