Objective To study the effect of dexmedetomidine(DEX)intrathecal administration on formation of chronic neuropathic pain induced by chronic constriction injury(CCI)in rats. Methods One hundred and twenty healthy adult male Sprague-Dawley(SD)rats were divided randomly into four groups(each n=30):sham group, model group,30μg/kg and 60μg/kg DEX intrathecal injection group(D30 group,D60 group). The CCI model was installed by left sciatic nerve ligaturing,sham surgery was done by exposing the sciatic nerve without ligation,and 30 μg/kg,60 μg/kg DEX(each,10 μl)and 10 μl normal saline were given intrathecally in D30,D60 and model groups respectively,all kinds of injection being once a day for 7 days. Hind paw mechanical contraction reflex threshold(MWT),heat-shrinkable reflex latency(TWL)and the score of motor dysfunction of hind extremity in rats were recorded on 1 day before ligation and 1,3,7 days after operation,and before ligation and 1,7,14 and 21 days after operation,the contents of tumor necrosis factor-α(TNF-α),interleukin(IL-1βand IL-6)in intumescentia lumbalis were measured by enzyme linked immunosorbent assay (ELISA). Results Compared with before operation,there were no significant differences in values of MWT,TWL,the motor function evaluation,TNF-α, IL-1β,and IL-6 at each time points(all P>0.05);however,with the prolongation of time,MWT and TWL were decreased,and the motor function evaluation,TNF-α,IL-1β,and IL-6 were increased in all the other groups. Compared with those of the sham group,MWT and TWL were declined,and the motor function evaluation,TNF-α, IL-1β,and IL-6 were elevated in model group. Compared with those of model group,30μg/kg and 60μg/kg DEX could significantly raise MWT(g)and TWL(s),obviously improve motor function and remarkably decrease the contents of TNF-α(pg/mg),IL-1β(pg/mg)and IL-6(pg/mg)in the spinal cord of CCI rats from 1 day after operation. And the changes in 60 μg/kg DEX group were more significant than those in 30 μg/kg DEX intrathecal injection group〔postoperative 1 day MWT:39.3±1.3 vs. 20.3±2.2,TWL:10.9±0.4 vs. 8.2±1.1,motor function score:2.00±0.00 vs. 2.00±0.75,TNF-α:33±7 vs. 125±18,IL-1β:108±12 vs. 203±34,IL-6:156±39 vs. 405±75,all P<0.05〕. Conclusions The DEX intrathecal administration has certain degree of dose-dependent therapeutic effect on hyperalgesia in CCI rat models. The mechanism is related to the amelioration of inflammatory reaction at the lumbar segment of spinal cord.