Abstract: Friction and wear properties of surface nanocrystallization of medium carbon steel were studied in dry sliding by a ring-on-disc tester. The wear weight loss and friction coefficient variation of specimens were analyzed. Wear behavior of surface nanocrystallization of medium carbon steel was discussed by surface topography. The resuits show that the friction coefficient of surface nanocrystallization specimens was markedly decreased at applied loads between 10 and 60 N, and its wear weight loss was reduced at applied loads between 10 and 40 N. The ob- servation of the surface topography shows that the nanocrystallization layer may reduce the effect of fatigue wear and improve the friction and wear properties of medium carbon steel.