Objective To explore the effect of different concentrations of iguratimod (IGU) on mouse model of bleomycin-induced pulmonary fibrosis.Methods A total of 108 female C57BL/6 mice were randomly divided into the control group,the model group,the low dose IGU group,the moderate dose IGU group,high dose with group and the methylprednisolone (MP) group (n=18 in each group).The mice in the control group were injected with 0.2 ml normal saline endotracheally,and others were injected with 0.2 ml bleomycin (5 mg/kg) from endotracheally to induce pulmonary fibrosis model.The next day,the mice in both control group and the model group were fed with 0.2 ml normal saline every day;The mice in the IGU groups and methylprednisolone group were fed with 0.2 ml iguratimod liquid the IGU (10,30,90 mg/kg) and 0.2 ml methylprednisolone (10 mg/kg) every dayrespectively.Finally the mice were sacrificed at day 7,day 14,day 28 respectively,and the lung tissue was examined by HE staining and Masson staining to evaluate the degree of alveolitis and fibrosis.Repeated measurement of variance analysis was used to compare the differences for time and group,and multi-factor analysis of variance LSD test was used for the comparison between groups.Results ① The body mass of mice in bleomycin-induced groups were decreased compared to the control group.② The pathological alveolitis scores in the high dose IGU group and methylprednisolone group were significantly decreased compared to those of the model IGU group at day 7 and day 14 (P＜0.05),and the pathological fibrosis scores were decreased dramatically compared with the model group at day 14 and day 28 (P＜0.05).Conclusion High concentration of IGU and methylprednisolone can reduce and inhibit lung inflammation and fibrosis of bleomycin-induced pulmonary fibrosis in mice.