Abstract: Formation and development of embryo sac in autotetraploid rice was carried out by WCLSM. The process of embryo sac formation and development in autotetraploid rice was similar to that in diploid rice, which could be divided into eight stages: archesporial cell formation stage, megasporocyte formation stage, megasporocyte meiosis stage, functional megaspore formation stage, mono-nucleate embryo sac formation stage, embryo sac mitosis stage, eight-nucleate embryo sac developing-stage, and embryo sac matured-stage. Some abnormalities in the development of embryo sac were founded in autotetraploid rice, including: cell degeneration, nuclei in abnormal position and number, the abnormal differentiation, and soon. These abnormalities would cause the abnormal structure of mature embryo sac.