Abstract: Objective To study the expression of heat shock proteins 70(HSP70),p53 and proliferation cell nuclear antigen(PCNA),and the mechanism of apoptosis induced by arsenic trioxide(As₂O₃)combined with hyperthermia in implanted liver cancer of rats.Methods The rat model of hepatocarcinoma was established and were randomly distributed into 4 groups including control group,which was treated with normal saline,As₂O₃ therapy group,which was treated with As₂O₃ at the concentration of 0.1% for 7d consecutively,hyperthermia group,which was treated with heat,and combination therapy group,which was treated with As₂O₃ combined with hyperthermia.After those treatments,the apoptosis,the expression of heat shock proteins 70(HSP70),p53 and the proliferation cell nuclear antigen(PCNA)in the cancer tissue were determined by histopathological examination and immuno-histochemical examination.Results The application of the combined treatment with As₂O₃ and hyperthermia,which induced a large number of necrotic and apoptotic cells in the cancer tissue,showed significantly higher anticancer effect than the use of As₂O₃ or hyperthermia separately.The expression of HSP70,p53 and PCNA was 30.12%±3.60%,27.64%±4.90% and 74.23%±6.35% in the control group.The expression of HSP70,p53 and PCNA was 87.41%±5.70%,90.06%±6.42% and 22.10%±6.17% in the group treated with the combination of As₂O₃ and hyperthermia.In the cancer tissue treated with the combination of As₂O₃ and hyperthermia,the expression of PCNA was significantly decreased(P=0.000 and P＜0.05),while the expression of HSP70 and p53 was significantly increased(P=0.000 and P＜0.05).Conclusion The results demonstrated that As₂O₃ and hyperthermia showed synergistic effect against liver cancer by inducing apoptosis and inhibiting the proliferation of cancer cells.These data implicated that the combination of As₂O₃ and hyperthermia could be an effective approach for the treatment of liver cancer.