Objective The aim of this study was to investigate the differences of the cell ultrastucture of normal mouse hatched blastocysts and their dormant ones cultured in vitro after freezing-thawing, and to explore whether the dormant embryos have a better anti-freezing shock property than the normal hatched mouse embryos. Methods By transmission electron microscopy, the ultrastructure of these two types of mouse embryos was observed and analyzed. Results By comparative analysis of their ultrastructure, the results showed that the dormant embryos before freezing are being austerity and with lower energy metabolism at a‘ground state'. After freezing-thawing and culture, their cellular structure seemed to be similar to that of the normal embryos cultured in vitro before freezing. However, after freezing-thawing and culture, the number of mitochondria decreased, the nuclei were loose, and their heterochromatin also increased. Conclusions From the ultrastructural observation, compared with the normal mouse hatched embryos, the cellular state of dormant mouse embryos after freezing-thawing is more favorable for material storage and energy metabolism, thus, indicating that they have a better anti-freezing property than normal hatched embryos.