Objective To investigate the effect of dexmedetomidine（DEX）on formaldehyde-induced acute inflammatory pain.    Methods  Thirty female ICR mice were randomly divided into three groups, including normal saline control (NS) group, formaldehyde（F）group and dexmedetomidine + formaldehyde (DEX+F) group. 0.1% formaldehyde solution was injected into subcutaneous tissue of mice right hind paw to establish acute inflammatory pain model. An hour before formalin injection, mice were intraperitoneal injected with DEX in DEX+F group, and mice were intraperitoneal injected with equal volume saline in NS group and F group. The expression of spinal cord glial fibrillary acidic protein (GFAP）, which is a astrocytes marker, was detected by immunohistochemistry and Western blotting.    Results  Spontaneous pain score showed that compared with the NS group, the F group had typical biphasic pain response; while compared with the F group, the DEX+F group showed a significant decrease in the first (P<0.001) and second phase pain (P<0.001). Immunohistochemical result  showed that compared with the NS group, the F group had an increase number of GFAP positive cells in the posterior horn of the spinal cord (P<0.001). However, the DEX+F group showed a decrease number of GFAP positive cells in the posterior horn of spinal cord compared with the F group (P<0.001). Western blotting result  showed that compared with the NS group, the F group had increased expression of GFAP in the spinal cord (P<0.05). Compared with the F group, the DEX+F group showed decreased GFAP expression in the spinal cord (P<0.05).    Conclusion  DEX may improve formaldehyde-induced acute inflammatory pain in mice by inhibiting the activation of astrocytes in the spinal cord.