Megasporogenesis and the development of female gametophyte in endangered Tsoonidendron odorum Chun were studied. The results showed that there were 2-5 ovules on the ventral surface of unicarpellate ovary wall. Ovules were anatropous, bitegminous and crassinucellar. Archesporial cell was one cell and differentiated from cell in the first or second layer beneath epidermis. The development of the embryo sac conformed to the Polygonum type. Abnormal development was observed at tetrad and mature embryo sac. Abnormal phenomena in the process of reproduction of Tsoongiodendron odorum causing this species to be endangered are discussed.