The screening tests for embryotoxicity in vivo are time-consuming and expensive when they are carried out on large number of laboratory animals. Because embryonic stem cell test(EST) may detect the influence of test compounds to the pluripotent and differentiation of stem cells, it is designed to discriminate test compounds of three classes of embryotoxicity: none, weakly and strongly embryotoxic. EST improves the correlation between the in vitro data and the in vivo data, and will be an alternative in vitro test for embryotoxicity in the future.