Abstract: Objective: To establish the murine Lewis lung carcinoma cell (LLC) line which can express the murine IL- 12 gene stably and to provide a basis for further study of its immunoregulatory mechanism and antitumor immune response. Methods: The recombinant plasmid containing the mIL12 gene was transfected by lipofection into the LLC cell line, and its expression in LLC cells was measured. Cell cycle and apoptosis were observed by FCM. The positive clone cells were obtained and cultured after selection with G418, and the activity of mIL- 12 was examined. Results: PcDNA3.1 (+)mIL- 12 plasmid was transfected into LLC cells successfully. RT- PCR and ELISA revealed that mIL12 showed high expression at the mRNA and protein levels and FCM revealed that the recombinant plasmid could promote LLC cell apoptosis. The T cell proliferation experiment showed that the culture supernatant of LLC/mIL- 12 cells could induce proliferation of murine spleen cells activated by ConA.Conclusion: A pcDNA3.1 (+)- mIL- 12 eukaryotic expression plasmid has been constructed correctly and the mIL- 12 in LLC cells has biological activity.