The biocompatibility of two dental casting alloys of Au-Ag-Pd-Cu was investigated by MTT assay. The cells morphology was observed with a phase-contrast microscope. In the experiment, the L-929 cell line and RPMI1640 with 5% FBS were used. The results show that the cell morphology is good, and the growth of cells is vigorous after the cells have been cultured and steeped in the two alloys for 3 days and 5 days. The cytotoxicity of two alloys was ranked as 0 ~ 1 with a good biocompatibility.