Objective: To investigate the adjuvant effect of intra-operative and postoperative low-dose ketamine administra-tion to remifentanil consumption in patient-controlled anal-gesia (PCA) for lower limb fracture.Methods: A total of 200 patients with lower limb frac-ture receiving the surgery were randomly divided into 4 groups. In Groups A, B and C, patients received 0.5 mg/kgketamine infusion under general anesthesia, and ketamine in a dose of 0.1 mg/kg, 0.05 mg/kg, 0.01 mg/kg per hour continuously for 24 hours after surgery, respectively. The control group (Group D) received an equivalent volume of normal saline only. With 20 μg/ml remifentanil in normal saline, postoperative PCA was administered with a back-ground infusion at 2 ml/h following 2 ml as a loading dose and 1 ml demand dose with a 3-minute lockout period. Remifentanil consumption, 11-point visual analog scale (VAS) scores, global satisfaction score (GSS), and side ef-fects were also recorded by the acute pain service. Results: Cumulative PCA remifentanil consumption in Groups A and B were (1378±377) μg and (1531±402) μg,significantly lower than (1807±510) μg and (1838±523) μg in Groups C and D (P<0.01). VAS scores in Groups A and B were significantly lower than those in Groups C and D (P<0.01). In the first 12 hours after operation, GSS was improved (P<0.01). No respiratory depression was observed. No significant dif-ference in side effects was observed among groups. Conclusion: Low-dose ketamine can relieve postop-erative pain and moderately decrease remifentanil consump-tion for PCA, with no obvious side effects of ketamine.