The seminiferous epithelium cycle and developmental stages of spermatids in Clethrionomys rufocanus were observed under a light microscope. The seminiferous epithelium cycle was divided into 8 stages. Type Ad spermatogonia appeared through all stages. Type Ap, In, and B spermatogonia appeared in stages Ⅰ, Ⅱ, Ⅲ, and Ⅳ. In the first meiosis prophase, the leptotene spermatocytes appeared from stage Ⅴ, the zygotene spermatocytes in stages Ⅰ, Ⅵ, Ⅶ, Ⅷ, the pachytene spermatocytes from stages Ⅱ to Ⅵ, the diplotene spermatocytes in stage Ⅶ. The meiotic figures and interkinesis spermatocytes were observed in stage Ⅷ. Developing spermatids were subdivided into 10 steps, based on the morphological characteristics such as the acrosome formation changes in spermatozoa, nucleus, cytoplasm, and spermiation changes. The C. rufocanus spermatocytogenesis and spermiogenesis results displayed similar results with Apodemus agrarius coreae and A. speciosus peninsulae. Considering all the results, the spermatogenesis may be useful information to analyze the differentiation of spermatogenic cells and the breeding season.