A/J mice injected with urethane(1mg/ g of body weight) develop tumors with distinct histological patterns, which are classified as solid and papillary. I divided the mice into 3 groups; control group treatment with saline, BA group treatment with herbal formula, Soeuminbojungikgitang 0.4g/kg and BA group treatment with herbal formula 2.0g/kg. The administration of herbal medicine was done every day for 8 weeks. The experimental results from herbal medicine treatment were compared to those from a saline-treated control group. Serial sections of the whole lung(150 to 200 sections per mouse) showed solid and papillary tumors arose from the pulmonary acinus, invading the bronchioles only as the tumors grew. The number of tumor, in the 8 weeks group, are decreased in the experimental groups compared to control group. COX-2 protein and IGF- I protein expression was more increased in lung tumors of the control group compared to BA and BB groups. These results suggest that Soeuminbojungikgitang extract suppress the carcinogenesis of lung in the A/J mouse.