This study investigated the effect of ultrasonic nanocrystal surface modification (UNSM) on the hardness and wear behavior of AISI STS316L at elevated temperatures. 316L stainless steel was treated by UNSM installed in CNC lath, and its hardness and wear behavior at elevated temperature were tested. Compared with the untreated sample (206 Hv), the hardness of the UNSM-treated sample was improved by 59% (328 Hv). Thus, at high temperature, even though the hardness both samples decreased, it was better for UNSM-treated samples. Further, the wear resistance of the UNSM-treated sample was superior to that of the untreated sample at room temperature, but the wear loss in UNSM-treated sample increased at 250℃ and 500℃. Meanwhile, the grain size of the UNSM-treated sample increased as the temperature increased. This is because the recrystallization temperature of UNSM-treated sample decreased, resulting in grain recovery due to the increase in temperature near the surface after repeated friction in a high temperature environment.