Abstract: To observe the spontaneous apoptosis of germ cells during the development of testis in mice,tests in situ are performed on the paraffin tissue slices of the testis at different developmental stages by the TUNEL detection,and 17 groups of Kunming normal mice are included.The results show that the spontaneous apoptosis is existed in the early postnatal mice testis.The number of apoptotic spermatogonia is increasing from the 1st to 15th day after birth;a few apoptotic primary spermatocyte is also observed on the 15th day;a few apoptotic secondary spermatocyte and round spermatids also appears on the 27th day;on the 30th day, apoptotic cells are only observed in spermatogonia;on the 33rd day, apoptosis occurrs in all types of germ cells; up to the 36th day,the apoptosis is focused on spermatogonia again and lasts during the whole subsequent stages.It indicates that the main apoptotic cells are spermatogonia at diverse development stages;the period of active apoptosis is from the 1st to 33rd day after birth,and is synchronous with the maturing process of primitive germ cells.