We analysed the karyotypes from bone marrow cells of the Japanese lesser horseshoe bat (Rhinolophus cornutus cornutus-5♂) and greater Japanese horseshoe bat (R. ferrumequinum nippon-2♂, 1♀) collected from Fukuoka Prefecture. The karyotypes are shown in Figs. 1 and 2. With regard to the genus Rhinolophus, Andersen (1905) discussed the phylogenetic relationships from the standpoint of external characters, i.e., especially the pattern of sella and wing, and dentition (cf. Figs. 3 and 4, Tables 1 and 2). We investigated the phylogeny proposed by Andersen with karyotypes of the horseshoe bats (R. cornutus, R. blasii, R. euryale, R. f. ferrumequinum, R. f. nippon and R. hipposideros) so far analysed (cf. Table 3 and Fig. 5). The mechanism considered responsible for karyotypic evolution in this genus is mainly centric fusion, which leads to a lowering of the diploid number with the concomitant formation of biarmed elements from uniarmed ones. Hence, the most primitive karyotype would be one which possessed the highest diploid number and in which all chromosomes were acrocentric. Therefore, it seems reasonable to assume that among them the most primitive form is R. cornutus whose autosomes are all acrocentric, being devoid of biarmed ones. The biarmed autosomes found in the above forms excluding R. cornutus could be classified into five types in size (Fig. 5). Considering the correlation between the length of their forearms and their karyotypes of the above forms, it seems likely that the larger body size characterizes the more evolved species (Fig. 6). Possible phylogenetic relationships in the genus Rhinolophus based on karyotypic data are depicted in Fig. 7. Our hypothesis agrees with Andersen's opinion, with the exception of a divergence of views on the phylogenetic position of the hipposideros group (cf. Figs. 4 and 7).