Abstract: Objective :To establish a Lewis lung cancer cell line modified by human mutant K-ras gene and investigate the biological characteristics of this cell line. Methods : K-ras/V12 gene was transfected into cultured Lewis lung cancer cell line by the lipofectin-mediated gene transfection method. The gene expression and proliferation characteristic of the transgenic cell were observed in vitro, and the ability of tumorigenesis was observed in vivo. Results : K-ras/V12 gene was successfully transfected into cultured Lewis lung cancer cell line by the lipofectin-mediated gene transfectionmethod. The transgenic cell had no significant difference with Lewis lung cancer cell line in grow curve and soft agar colony forming rate. This cell had higher expression level of p21 and had higher ability of tumorigenesis in C57BL/6 mice. Conclusion : The K-ras/V12 modified Lewis lung cancer cell line is successfully established.