Abstract: 【Objective】 To investigate the expression of matrix metalloproteases 9 (MMP-9) in dorsal root ganglion (DRG) in remifentanil-induced hyperalgesia. 【Methods】 Hyperalgesia was induced by intravenous infusion of remifentanil 4 μg/kg/min for 0.5 ~ 2 h and MMP-9 inhibitor was intrathecally administered 30 min before remifentanil infusion. Nociception was assessed using Von Frey test and Hargreaves methods after remifentanil infusion from the 2nd hour to the 5th day and the expression of MMP-9 in dorsal root ganglion (DRG)was observed with immunohistochemistry and Western blot analysis. 【Results】 Intravenous infusion of remifentanil led to significant reduction of sensory threshold and pretreatment with MMP-9 inhibitor could attenuate hyperalgesia induced by remifentanil. Immunohistochemistry and Western blot results showed that MMP-9 expression was significantly upregulated in the DRG in remifentanil hyperalgesia rats. 【Conclusions】 High MMP-9 expression in DRG could be suggestive of a underlying mechanism of hyperalgesia induced by remifentanil.