The classification of the cycle of the seminiferous epithelium was carried out in the common tree shrew (Tupaia glis). The tree shrew captured in Thailand were fixed with Bouin's fixative, embedded in paraffin wax, and stained with PAS-hematoxylin. The cycle was classified into twelve stages on the basis of the acrosomal changes of spermatids. Relative frequencies of stages form I to XII were 11.9, 7.2, 8.9, 22.5, 12.9, 9.7, 8.0, 5.9, 4.0, 3.2, 2.9, and 3.6%, respectively. Different stages did no appear in a cross-sectioned tubule as did in primates. The head of matured spermatid was discoidal in shape and different from that of primates and rodents. Spermatogenesis of the common tree shrew is different from that of primates and rodents according to its morphological features.