|To investigate the process of spermiogenesis of the Korean eastern Daubenton뭩 bat, Myotis aubentonii ussuriensis, the testis obtained from mature male bats was studied by transmission electron microscope and were based on the variety and diagnostic characters of cell organells. The results obtained from the pres-ent study are as follows. Accroding to the differentiation of the cell organells, the spermiogenesis of the Korean eastern Daubenton뭩 bat, M. d. ussuriensis, was divided into Golgi, cap, acrosome, maturation and spermiation phases. Besides, these Golgi, cap, acrosome, and maturation phase were subdivided into the steps of early and late phases respectively and maturation phase was subdivided into step of early, mid and late phases. Therefore, the spermiogenesis of M. d. ussuriensis has been divided into a total of 11 phases. The chromatin granules began to condense at the early cap phase, regularized at the acrosome phase, and a perfect nucleus of sperm was formed at the maturation phase. The chromatoid body was oc-curred in the upper cytoplasm of nucleus at the early Golgi phase, and it was accurred the posterior cyto-plasm of the nucleus at the early maturation phase. The formation of sperm tail began to be develop in the early Golgi phase, and completed at the spermiation phase. The fiber structure of middle piece was consisted of nine outer doublets and two central singlet microtubules and Nos. 1, 5, 6 and 9 in the outer dense were larger than the others(2, 3, 4, 7, 8).