Objective To investigate the effects of ketamine on the hyperalgesia induced by remifentanil in a rat model of postoperative pain. Methods sixty SD rats were randomly divided into 5 groups(n=12 each):control group (C); incisional pain group (I); ketamine group (K); remifentanil group (R); ketamine+ remifentanil group (K+R). A right hind paw plantar incision was performed in groupI, K, R and K+R. ketamine (10 mg/kg) was injected subcutaneously 30 min before plantar incision In group K and K+R. In group R and K+R ,remifentanil (0.04 mg/kg) were infused subcutaneously with a pump for 30 min at the moment of surgical incision. All rats were anesthetized with sevoflurane. The paw withdrawal mechanical threshold(PWMT)and paw withdrawal thermal latency(PWTL) were used to evaluate the behavioral changes and measured at 24 h before incision and at 2 h,6 h,24 h and 48 h after incision. Results Results Compared with group C and baseline, the decrease of PWMT and PWTL were observed at 2, 6, 24, 48 h after incision in groupI；Compared with group I, the significant decrease of PWMT(6.48±1.23 g) and PWTL(11.13±1.95 s) were observed at 2 h after incision in group R, and this level continued until 48 h after incision; Compared with group R, the significant increase of PWMT（9.36±1.76，9.41±1.50，10.18±1.42，10.15±1.48）g and PWTL（15.66±2.42，16.24±2.55, 15.13±3.07, 15.66±2.44）s were observed at 2 h,6 h,24h and 48 h after incision in group K+R. Conclusion ketamine pretreatment prevents the development of hyperalgesia induced by remifentanil in a rat model of postoperative pain.Conclusion ketamine pretreatment prevents the development remifentanil-induced hyperalgesia in postoperative paina rat model.