Objective: To investigate the role of monocarboxylate transporter-2 in spinal dorsal horn in rat of postoperative chronic pain. Methods: 76 male SD rats were divided randomly into 3 groups: sham group (group S0), SMIR model group (group S1) and 4-CIN group (group S2). Group S1 and S2 were operated with the model of persistent postoperative pain induced by skin/muscle incision and retraction; group S0 were treated as sham operated rats. Ten days after operation, group S2 received intrathecal injection of 100μmol 4-CIN dissolved in 10% DMSO 10μl, while group S1 received intrathecal injection of 10% DMSO 10μl only. The paw withdrawal mechanical threshold (PWMT) was tested 1d before operation and 1d,3d,7d,10d,14d,21d,28d after operation. In group S0 and S2, 4 rats were killed on 14d. In group S1, 4 rats were sacrificed at each time point. The L4-5 segment of spinal cord was removed, in order to measure the expression of monocarboxylate transporter-2 by Western blot analysis. Results: The basic values of PWMT before operation had no statistically significant differences among three groups（P＜0.05）.The PWMT in group S1 were significantly lower from 3d (10.7±3.4，P＜0.05) to 28d (10.6±2.5，P＜0.05) when compared with group S0, while the MCT-2 expression in spinal dorsal horn on 1d~28d were significantly higher in group S1 than in group S0. The MCT-2 expression on 14d was significantly lower in group S0 and S2 than in group S1.Conclusion: The level of monocarboxylate ransporter-2 in spinal dorsal horn is significantly up-regulated in a rat model of SMIR. Intrathecal administration of 4-CIN can attenuate persistent postoperative pain in rats induced by SMIR and it may through reducing the increase in MCT-2 expression in spinal dorsal horn.