Objective: To investigate the effect of IFNα on doxorubicin-induced apoptosis in human osteosarcoma cells with its molecular mechanisms to provide evidences for improving the treatment of osteosarcoma. Methods: Osteosacoma U2OS and MG63 cells were treated with IFNα and Doxorubicin, alone or in combination, for 72 h . Cytotoxicity was determined with MTT. Apoptosis was evaluated through fluorescence-activated cell sorting, Hoechst33258 staining and DNA ladder assay. The expression of p53, Bax, Bcl-2, Mdm2, p21, caspase-3 and PARP was determined with Western blot. siRNA interference was used to silence p53. Results: IFNα treatment for 72 h did not induce cytotoxicity but greatly enhanced doxorubicin-induced cytotoxicity and apoptosis in p53-wild U2OS cells but not p53-mutant MG63 cells. Compared with other groups, the combination of IFNα and doxorubicin induced more obvious apoptotic morphological changes and DNA ladder. IFNα did not alter the expression of the indicate genes. The expression of p53, Bax, Mdm2 and p21 was up-regulated by doxorubicin and further increased in response to combination. The expression of Bcl-2 was down-regulated by doxorubicin and further decreased in response to combination.There were no differences among groups in MG63 cells. The expression of p53 was effectively blocked by p53-siRNA in U2OS cells. The p53 silencing greatly reduced the cytotoxicity mediated by combination for 72 h, compared with non- and control-siRNA groups. The activation of caspase-3 and PARP mediated by combination was largely suppressed by p53 silence. Conclusion: IFNα sensitizes human osteosarcoma cells to doxorubicin-induced apoptosis through p53-dependent pathway. The combination of IFNα and traditional chemotherapy can be used in osteosarcoma treatment.