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AIM: To construct a pEgr-IFNγ plasmid and to investigate its expression properties of interferon-γ (INF-γ) induced by irradiation and the effect of gene-radiotherapy on the growth of melanoma.METHODS: A recombined plasmid, pEgr-IFNγ, was constructed and transfected into B16 cell line with lipofectamine. The expression properties of pEgr-IFNγwere investigated by ELISA. Then, a B16 melanoma-bearing model was established in mice, and the plasmid was injected into the tumor tissue. The tumor received 20 Gy X-ray irradiation 36 h after injection, and IFN-γ expression was detected from the tumor tissue. A tumor growth curve at different time points was determined.RESULTS: The eukaryotic expression vector, pEgr-IFNγ,was successfully constructed and transfected into B16 cells.IFN-γ expression was significantly increased in transfected cells after X-ray irradiation in comparison with 0 Gy group (77.73-94.60 pg/mL, P＜0.05-0.001), and was significantly higher at 4 h and 6 h than that of control group after 2 Gy X-ray irradiation (78.90-90.00 pg/mL, P＜0.01-0.001).When the transfected cells were given 2 Gy irradiation 5 times at an interval of 24 h, IFN-γ expression decreased in a time-dependent manner. From d 3 to d 15 after IFNγ generadiotherapy, the tumor growth was significantly slower than that after irradiation or gene therapy alone.CONCLUSION: The anti-tumor effect of pEgr-IFNγgeneradiotherapy is better than that of genetherapy or radiotherapy alone for melanoma. These results may establish an important experimental basis for gene-radiotherapy of cancer.