Abstract: Objective To investigate the effect of melatonin (MT) on signal transduce and activator of transcription 4（STAT4）and its airway inflammation in asthmatic mice. Methods At 1h after the last aerosol exposure, the left lungs were lavaged, the number of inflammatory cell in the mouse bronchoaleolar lavage fluids (BALF) were counted with microscope. Using immunohi- stochemistry and real-time fluorescent quantitative PCR to detect expression of STAT4 protein and its mRNA expressionism in right lung tissue. Using enzyme-linked immunosorbent assay to detecte levels of IL-12 in serum. Results (1) In model group, the number of inflammatory cells and EOS were significantly higher than control group, STAT4 protein and STAT4mRNA expression in lung tissue was significantly decreased when compared with control group. MT treated group significantly alleviated the above-mentioned parameters.And there were significant differences between MT treated group and control group,DXM treated group and model group. (P＜0.01). (2)In asthmatic mice, STAT4 protein and its mRNA expression had both altitude negative relationship with EOS counts in BALF (r=0.849, P<0.01; r=0.972, P＜0.01, respectively). Levels of IL-12 in serum had altitude positive correlation with STAT4 protein expression in asthmatic group mice(r=0.742, P＜0.01). Conclusion MT may be through inducing STAT4 gene transcription and translation in asthmatic mice, promoting production of IL-12 in peripheral blood,inhibiting inflammatory cell infiltration,significantly reduce the airway inflammation.