Objective To explore the anti-tumor effects of Egr-IFNγ gene therapy combined with 125I-UdR radionuclide therapy in mice bearing H22 hepatocarcinoma and its mechanism. Methods The recombinant plasmid pcDNAEgr-IFNγ mixed with liposome was injected into tumor. 48 h later, 370 kBq 125I-UdR was injected into tumor. The tumor growth rates at different times were observed. After 3 d gene-radionuclide therapy, the concentration of IFNγ in cytoplasm of H22 cells and cytotoxic activities of splenic CTL of the mice in different groups were examined. Results The tumor growth rates of pcDNAEgr-IFNγ +125 I-UdR group were obviously lower than those of control group, 125I-UdR group and pcDNAEgr-1 +125I-UdR group 6-15 d after gene-radionuclide therapy. IFNγ protein was found in cytoplasm of H22 cells in PcDNAEgr-1FNγ+125I-UdR group after 3 d gene-radionuclide therapy. Cytotoxic activity of splenic CTL in pcDNAEgr-IFN7 + 125I-UdR group was significantly higher than that in the other groups (P<0.01). Conclusions The anti-tumor effects in vivo of pcDNAEgr-IFNγ gene therapy combined with 125I-UdR radionuclide therapy are better than those of 125I-UdR therapy.