An experimental study on the influence of thermal aging on the friction and wear properties of a nitrile butadiene rubber (NBR)-steel pair was carried out. Rubber specimens were aged in hydraulic oil at 60 degrees C and 90 degrees C for 0-70days. The Shore hardness, Young's modulus, rebound resilience, and other mechanical properties were measured. The friction coefficient and wear volume were tested to evaluate the tribology performance. To investigate the mechanism of NBR thermal aging, the molecular structure and crosslinking degree were analyzed. Crosslinking with rubber aging in oil led to differences in the physical and mechanical properties. The Shore A hardness decreased initially and then increased. The Young's modulus increased and the rebound resilience decreased. The friction coefficient increased but the wear volume decreased with aging time. These differences affected the friction and wear behavior of the NBR against the steel shafts and resulted in sealing-ring degradation and failure.