Abstract: To establish an effective method for identifying the vitality of mouse embryos, the embryos were stained with trypan blue in different concentrations diluted by PBS （1：6, 1：4，1：3, 1：2，1：1，1：0） and cultured separately for each group. The results revealed that the developing rates were 70.7%,66.5%,77.0%,60.0%,45.0% and 30.0% respectively. The results suggest that the 1：3 staining concentration is optimal. It was further confirmed by the electron microscopy.