Abstract: Objective: To observe the effects of intrathecal(IT) morphine on incisional pain and expression of c-fos in spinal cord of rats with postoperative pain.Methods: In a rat model of postoperative pain,the cumulative pain scores were used for evaluating pain behaviors.Immunohistochemistry technique was involved in observing the expression of c-fos in slices of spinal cord of rats.Results: In control group,cumulative pain scores were significantly higher than that in sham-operation rats 2 hours,24 hours and 48 hours after incision and at the same time,compared with that in control group,cumulative pain scores in treatment groups were significantly lower(P<0.01).There was no significant difference among treatment groups administered with drugs either before or after incision(P>0.05).Seventy-two hours after incision,there was no significant difference in cumulative pain scores among operative groups(P>0.05).From 96 hours to 120 hours after incision,there was no significant difference among all groups(P>0.05).IT morphine given either before or after incision decreased the number of Fos-LI neurons significantly in dorsal horn of spinal cord 2 hours after incision(P<0.01).IT morphine given before incision decreased the number of Fos-LIl neurons more effectively than that after incision.From 24 hours to 120 hours after incision,there was no significant difference among all operative groups(P>0.05).Conclusions: In a rat model of postoperative pain,IT morphine administered either before or after incision provides analgesia and inhibits the Fos protein expression only in early period after incision.