In most lower termites, colonies are headed by neotenic reproductives after the primary reproductives died. In such cases, termites have the neotenic castes of both males and females, although a few species show unequal frequencies of male and female neotenics. However, some species of Neotermes [Kalotemitidae] show exclusive maleness in the neotenic caste. We found that N. koshunensis in Okinawa also show exclusive maleness in the neotenic caste. When colonies were orphaned in the laboratory, the neotenics produced were always males. Moreover, the neotenic caste differentiation of the species did not follow the schema presented by Lüscher (1961), in which the rising of the male and female neotenics is inhibited by the presence of the primary reproductive of the same sex. The schema suggests that a neotenic caste would rapidly occur in the colony when either sex of the primary reproductives died. However, in the N. koshunensis, the male neotenic is inhibited completely not only by the presence of the primary king but by the presence of the primary queen. Therefore, it seems to be difficult for N. koshunensis colonies to recover the reproductive pair. Male neotenics emerged in the laboratory did not have a spermatozoid nucleus in their spermaducts. The social role of the male neotenics in N. koshunensis is quite puzzling.