Abstract: To evaluate the therapeutic effects of IFN- γgene transfer compared to intratumoral injection of recombinant IFN- γin tumor- bearing mice. Methods: Balb/c mice were used as the animal model and were inoculated subcutaneously with colon cancer cell line CT26. The tumor-bearing mice were divided into five groups (9 mice in each group) and were treated with different methods. A mixture of pcDNA3-huIFN- γ, a eukaryotic expression vector containing the full-length IFN- γgene, and lipofectamine was injected intratumorally twice into the mice in Group A with a oneweek interval. In Group B, the tumor-bearing mice received intratumoral injections of recombinant IFN- γdaily for 4 weeks. In Group C, the recombinant IFN- γwas administered three times per wee for four weeks. In Group D, the mice were injected with saline daily for 4 weeks. Parent pcDNA3 vector injection was conducted in Group E to serve as the control. The empty vector injection was repeated after one week. The tumor volume was measured and the tumor tissues were removed and collected for pathological examination and flow cytometry analysis. Results: Tumor regression was conspicuous in Group A, B and C, compared to group D and E. Excess lymphocyte infiltration of the subcutaneous tumors can be seen microscopically in Group A, B and C and the percentage of CD3+ and CD4+ T- lym-phocytes was significantly higher in those groups than that in Group D or E based on flow cytometry data. Conclusion: IFN- γexpressed by the vector had an inhibitory effect on tumor growth in tumorbearing mice. The therapeutic effect of the group treated with the IFN- γvector is identical to that of the group that received daily intratumoral rIFN- γinjections, but it is better than that of the group that received intermittent rIFN- γinjections.