The Nintendo Wii racer has climbed from seventh spot last week to hit the front in Germany, while a three place climb is noted in Spain.
Need for Speed: Undercover has also improved its position in Germany, moving into second, with Wii Fit, World of Warcraft: Wrath of the Lich King and Call of Duty; World at War completing the top five.
In Spain, it is Wii Play that has emerged in second spot, followed by Pro Evolution Soccer 2009, Need for Speed: Undercover and Wii Fit.
Mario Kart Wii gamers are given the choice of selecting from 24 characters, separated into three weight classes, which help to determine the type of kart available to them.
Some 12 racers are available from the start while others become unlocked when certain tasks have been completed.
Among the characters available to gamers are Mario, Luigi, Donkey Kong and Yoshi.