Gastone Nencini (Italian pronunciation: [ɡaˈstoːne nenˈtʃiːni]; 1 March 1930 – 1 February 1980) was an Italian road racing cyclist who won the 1960 Tour de France and the 1957 Giro d'Italia.

Nicknamed Il Leone del Mugello, "The Lion of Mugello" (from his birthplace Barberino di Mugello, near Florence), Nencini was a powerful all-rounder, particularly strong in the mountains.

He was an amateur painter and a chain smoker. He was a gifted descender. "The only reason to follow Nencini downhill would be if you had a death wish", said the French rider Raphaël Géminiani. It was in trying to follow Nencini down a mountain on Stage 14 of the 1960 Tour de France that Roger Rivière missed a bend, crashed over a wall and broke his spine.