Abstract: Objective To investigate the therapeutic effects of different doses of buprenorphine combined with morphine on bone cancer pain in a rat model. Methods Female adult Wistar rats were selected for this experiment. After Walker256 rat breast cancer cells were subcutaneously injected into the left tibia of the rats to induce bone cancer pain, the model rats were divided into 5 groups (n=8 for each): M (mophine 10 mg/kg), MB1(morphine 10 mg/kg+ buprenorphine 20 μg/kg), MB2 (morphine 10 mg/kg+ buprenorphine 40 μg/kg), MB3 (morphine 10 mg/kg+ buprenorphine 60 μg/kg) and Sham (isotonic saline 1 ml). Morphine and/or buprenorphine were subcutaneously given twice a day (at 7:00 am and 7:00 pm, respectively) for 7 consecutive days. From day 15, all rats underwent behavioral pain tests including tail flick test, mechanical pain sensitivity test and thermal pain sensitivity test 30 min before and after drug adminstration at 7:30 am. Results Antinociceptive and mechanical pain threshold showed no significant difference between MB groups and M group. The presence of significant decrease in thermal pain threshold in MB2 group was later than that in M group (6th day vs. 5th day). Conclusion In the treatment for cancer pain in rats, the combination of morphine and buprenorphine has similar antinociceptive effect to morphine, moreover, it may delay morphine tolerance.