They performed a medley of rap hits on "Late Night With Jimmy Fallon" Wednesday night, and the clip is becoming a viral hit.
Fallon and Timberlake started off with Sugarhill Gang's classic "Rapper's Delight" and went on to perform jams from the Beastie Boys, the Notorious B.I.G., Jay-Z and Eminem.
The 36-year-old Fallon says he's surprised by the skit's success. Fallon says he took time to get it right before taking the stage.
Fallon says that "you know I really needed to practice" because "you know I can't rap." He says that he was rehearsing in his apartment "till 2 in the morning" and that his wife called him crazy.
The NBC show's house band The Roots backed them up.