Sonu, 40, will belt out some hit numbers while Big B will jive to its beats.
"With the incomparable Sonu Nigam and the fluidity of his voice...still trying desperately to shake that b**ty," Big B posted on his blog.
Except for the third season, which was hosted by superstar Shah Rukh Khan, Amitabh has been the quiz master of the show since the beginning, but is still nervous about the premiere episode of the seventh season.
"Setting up for the opening of KBC on September 6, the 7th season, and the excitement and the nervousness mounts, but giving it all that it deserves tasseled shoes and all," he posted.
The show, based on international quiz show "Who Wants To Be A Millionaire", first went on air in 2000.