The 32-year-old actor said his first thought on hearing the news was, "Y'all are messing with me."
Tatum's film roles include "Magic Mike" and the upcoming "Foxcatcher," where he'll play an Olympic athlete.
People announced its 2012 list Wednesday morning.
Actor Bradley Cooper took last year's sexiest man title. Others who have won the honor include George Clooney, Matt Damon, Brad Pitt, Johnny Depp and Ryan Reynolds.