Four-ball tribological apparatus was employed to investigate the sliding wear behavior of bearing steel 52100 treated by salt bath itrocarburizing and complex nitrocarburizing processes. The microstructures, phase identification, surface hardness and hardness profiles of specimens were analyzed by optical microscopy, X-ray diffraction and microhardness testing. The experimental results show that higher sub-surface hardness and hardness profiles were obtained by nitrocarburizing and complex nitrocarburizing, although their surface hardness was lower than that of commercial balls. It was also demonstrated that the o-phase formed on the specimen surfaces had a significant effect on reducing friction coefficient but this treatment lowered the wear resistance. Complex nitrocarburizing increased the wear resistance. Both Nitrocarburizing and complex nitrocarburizing could upgrade the load-bearing capacity of treated specimens.