OBJECTIVE： To study the inhibitory effect of modified Maimendong decoction combined with cisplatin on Lewis lung cancer transplantation model mice， and to explore its potential mechanism. METHODS： Lewis lung cancer transplantation mice model was induced via subaxillary inoculation of Lewis lung cancer cells. 60 mice were randomly divided into model group （normal saline， once a day， i.g.）， cisplatin group （6 mg/kg， once a week， i.p.）， modified Maimendong decoction group （20 g/kg. once a day， i.g.） and combination group （cisplatin 6 mg/kg， once a week， i.p.+modified Maimengdong decoction， once a day， i.g.）， with 15 mice in each group. All mice were treated for consecutive 2 weeks. After medication， tumor weight and thymus index were detected； HE staining was used to observe the pathological change of tumor tissue. TUNEL was used to detect apoptotic index of tumor tissue. The protein expressions of Bcl-2 and Bax were detected by Western blot assay. RESULTS： Compared with model group， tumor weight and protein expression of Bcl-2 were decreased significantly in modified Maimengdong decoction， cisplatin group and combination group （P＜0.05）， and thymus index， tumor apoptotic index and the protein expression of Bax were increased significantly （P＜0.05）. Tumor weight and protein expression of Bcl-2 in combination group were significantly lower than modified Maimengdong decoction group and cisplatin group （P＜0.05）； thymus index， tumor apoptotic index and the protein expression of Bax were significantly higher than addition and subtraction of modified Maimengdong decoction group and cisplatin group （P＜0.05）. HE staining showed that the density of tumor cells was decreased to certain degree in modified Maimengdong decoction group， cisplatin group and combination group； the area of necrosis area in the combination group was significantly larger than in modified Maimendong decoction group and cisplatin group. CONCLUSIONS： Modified Maimendong decoction can inhibit the growth of Lewis lung cancer transplanted tumor in mice by down-regulating the protein expression of Bcl-2 and up-regulating the protein expression of Bax.