Abstract: This study examined anesthetic behaviors of Schizothorax o’connori Llord in two size ranges as induced by MS-222, to acquire useful information on anesthesia of said highland fish species in out-of-water activities (surgery, labeling, measurement, etc.). Test results indicated that for both large (25.0±1.5) cm and small-sized (14.8±2.3) cm specimens, respiration rates showed no significant change in anesthetic stages Ⅰ to Ⅲ, and only begun to significantly decline after entering stage Ⅳ. The effective concentrations of MS-222 were 150—180 mg/L and 150 mg/L for two sizes, respectively. The 150—180 mg/L caused large specimens to enter anesthetic stage Ⅳ within 5min, and recovered within 5min; the 150 mg/L caused small specimens to enter stage Ⅳ within 5min, and recovered within 7min; both doses ensured a 100% survival rate after immersion for 20min. For large specimens anesthetized at 180 mg/L for 5min and exposed to air for 0—15min, there was no significant difference in recovery times (P>0.05); for small specimens anesthetized at 150 mg/L for 5min and exposed to air for 0—15min, there were significant differences in recovery (P<0.05).