Abstract: Objective To evaluate the analgesic effects of centipede-scorpion powder(CS) on cancer-induced bone pain of rats and observe the expression of c-fos protein expression in spinal dorsal horn in rat with bone cancer pain. Methods Female Sprague-Dawley rats were randomly divided into 6 groups:Sham group(group S), Cancer group(group A), Normal saline group(group NS), 20 mg/kg CS group(group C₁), 40 mg/kg CS group(group C₂), and 80 mg/kg CS group(group C₃). The model rats were injected Hank's solution(10 μl, 2×10⁷ cells/ml) into the left tibia medullar cavity. The mechanical withdrawal thresholds were measured on left hind paws after using different doses of CS for bone cancer pain in rat for 4 days at 9th day after modeling. The L₄, L₅ segment of the spinal cord was removed for determination of the expression of c-fos by Western Blotting, and c-fos mRNA expression by reverse transcriptase-polymerase chain reaction(RT-PCR) in the spinal dorsal horn. Results Compared with group S, the mechanical pain threshold was decreased in groups A at 9th, 12th days after modeling, the difference were all statistically significant[the mechanical pain threshold at 9th day respectively:(8.69±0.53) g vs. (6.61±0.22) g, P<0.05; the mechanical pain threshold at 12th day, respectively:(8.67±0.43) g vs. (6.56±0.48) g, P<0.05]; And the expression of c-fos protein, c-fos mRNA were increased in groups A at 12th day after modeling, the difference were all statistically significant[protein level, respectively:1.46±0.19 vs. 3.61±0.51, P<0.05; mRNA level respectively:0.65±0.22 vs. 2.53±0.31, P<0.05]. Compared with group NS, the mechanical pain threshold was increased in groups C₂ and C₃ at 12th day after modeling, the difference were all statistically significant(all P<0.05); And the expression of c-fos protein, c-fos mRNA were decreased in groups in groups C₂ and C₃ at 12th day after modeling, the difference were all statistically significant(protein level respectively:3.24±0.67 vs. 2.71±0.43, 2.15±0.37, P<0.05; mRNA level respectively:2.39±0.44 vs. 1.62±0.21, 1.46±0.14, P<0.05). Conclusion Centipede-scorpion powder can alleviate hyperalgesia in bone cancer rats, its mechanism may be related to down-regulation of c-fos expression in spinal dorsal horn.