Objective:To evaluate the biocompatibility of two dental alloys (Au alloy and Ni-Cr alloy )and to investigate effects of two alloys expression of Bax and Bcl-2 of mouse fibroblast cells L929,try to find a new experimental method to evalute the biocompatibility of dental materials at molecular level. Methods: The fibroblast L929 cells were treated with leaching liquids of Au alloy (groupA) and Ni-Cr alloy (groupB),the RPMI 1640 cell medium containing 10% fetal calf serum was served as a negative control(groupC). The cytotoxicities of two alloys was evaluated by MTT and their effects on the expression of Bax and Bcl-2 were examined by immunohistochemistry and ELISA method. Results: The cytotoxicity of two alloys was in Grade 0,the ratio of Bax/Bcl-2 was higher in Ni-Cr alloy group than that of other groups,and the differents were significant. Conclusion:The results suggested that the leaching liquids of Ni-Cr alloy may induce Bax protein expression and Bax/Bcl-2 ratio increase;the results may provide new ideas for the future evaluation of biotic materials for compatibility at the molecular leval.