Abstract: Objective To develop a lung tumor model induced by benzo(a)pyrene(B(a)P)in male Kunming mice,and investigate the effect of estradiol(E2)on B(a)P-induced lung tumorigenesis.Methods Kunming mice were exposed to B(a)P and E2(once a week)for 8 weeks,followed by a recovery period of 8 weeks.At the termination of experiments,mice were killed to harvest lung tissues for morphological and pathological diagnosis to identify lung tumors.The levels of serum superoxide dismutase(SOD)and malondialdehyde(MDA)were also detected.Results The tumor incidence and multiplicity of the B(a)P group and the B(a)P+E2 group were significantly higher than those of the control group and the E2 group(P<0.05).The tumor incidence and multiplicity of the B(a)P group were higher than those of the B(a)P+E2 group with significant difference in tumor multiplicity(P<0.05),yet no significant difference in tumor incidence(P>0.05).The levels of serum MDA were 9.578±1.059,8.946±1.037,8.739±1.374,81536±01695 in B(a)P group,B(a)P+E2 group,E2 group and control group respectively.While the levels of serum SOD were 180.529±16.776,189.205±16.522,193.548±13.376,198.992±17.307 in those groups respectively.Conclusion A lung tumor model induced by B(a)P in male Kunming mice was developed,E2 may decrease the tumor multiplicity of B(a)P induced lung tumors in male Kunming mice by modulating lipid peroxidation and augmenting antioxidant defense system.