Objective:To study the regulation of matrine on Th1/Th2 mechanism of Pseudomonas aeruginosa(PA)infected lung in rats. Methods40 SD rats of clean grade were randomly divided into the normal control group,PA model group,matrine group,levofloxacin group and combination group,8 rats in each group. After anaesthesia,the model was established by PA injection with bronchial intubation,while the normal control group was treated with normal saline instead of PA. Each group was treated with the corresponding intervention. The pathological changes of lung tissue were observed. The contents of interleukin-4(IL-4) and interferon-γ(IFN-γ) in lung tissue were detected by ELISA,the protein expressions of T-bet and Gata-3 were determined by Western blot,and the mRNA expressions of IL-4,IFN-γ,T-bet and Gata-3 were detected by semi-quantitative RT-PCR.  Results:Compared with the PA model group,the content and mRNA expression of IL-4 in lung tissue were decreased in the matrine group,levofloxacin group and combination group,while the content and mRNA expression of IFN-γ were increased(P<0.05). Compared with the PA model group,the protein and mRNA expressions of Gata-3 in lung tissue were decreased in the matrine group,levofloxacin group and combination group(P<0.05),while the protein and mRNA expressions of T-bet were increased(P<0.05).  Conclusion:Matrine can regulate the expressions of transcription factor T-bet and Gata-3 in lung of rats with Pseudomonas aeruginosa infection,induce the differentiation from Th2 to Th1,promote IFN-γ synthesis and inhibit IL-4 synthesis,and thus reduce the pathological infection of lung.