The cycle of the seminiferous epithelium and the development of spermatids of Apodemus agrarius coreae were observed using a light microscope. The cycle of the seminiferous epithelium was divided into 10 stages, and developing spermatids were subdivided into 10 steps. The Golgi phases occurs the first two steps ($St_1,;St_2$), and the cap phases had the next two consecutive steps ($St_3$ and $St_4$). The acrosomal phases consisted of steps $5{sim}8$ ($St_5-St_8$), and the remaining two steps consisted the maturation ($St_9$) and spermiation ($St_{10}$) phases, respectively. Type Ad spetmatogonia are appeared in all stages (I-X). Type Ap spermatogonia appeared from stage I and II, In spermatogonia from stage III, IV and V, and B spermatogonia from stages VI. The leptotene spermatocytes appeared from stage VII, zygotene from stages I, II, VIII, IX and X, pachytene from stage III to VIII, diplotene in stage IX, and meiotic figures and secondary spermatocytes in stage X. These data are considered in relation to interspecific differences in sperm morphology.