Objective:To observe the immunoreactive changes of P2X3 receptor and examine P2X3 receptor mRNA level in the dorsal root ganglia (DRG) in a rat model of bone cancer pain. Methods: Sixty female Wistar rats, weighing 150-200 g, were randomly allocated to three groups (n=20 each): group CP (cancer pain) received intra-tibial injection of Syngeneic Walker 256 mammary gland carcinoma cells (2×105 ), group S received intra-tibial injection of equal volume 0.9% sodium chloride, and group C received blank control. Mechanical allodynia and thermal hyperalgesia tests were taken on 4, 7, 10, 14, 17, and 21 days after inoculation. On day 14 and 21, ten rats of each group were chosen for either immunohistochemistry or real-time RT-PCR to examine the changes of P2X3 receptor and mRNA. Results: The rats in group CP began to display hyperalgesia on day 10 and the pain became most obvious between day 14 and 21. Immunohistochemistry showed that the proportion of DRG neurons positive of P2X3 receptor in group CP was significantly increased on 14 and 21 d(P<0.05), and RT-PCR showed that the expression of P2X3 receptor mRNA was also significantly increased. Conclusion: These results suggest that our rat model of bone cancer pain has hyperalgesia, which might be related to the increase of P2X3 receptor expression.