In termite species of the family Kalotermitidae, most colonies usually have a 1:1 sex ratio. However, in the dry-wood termite Neotermes koshunensis (Shiraki) [Kalotermitidae], we found male-biased sex ratio for pseudergates, nymphs, alates, and soldiers in the colony. The bias was not related to the swarming season and to the colony size. Males were 0.9- 1.7% larger than females in head width, thus confirming male-biased sex allocation in this species. It seemed that the male-biased sex allocation was not explained by Local Resource Competition model or by Local Resource Enhancement model. Our results together with the previous studies suggest that the sex ratio bias in the genus Neotermes is correlated with sex specificity in colony succession by secondary reproductives (neotenics): male-biased sex ratio is typically observed in the species with male neotenics only. We need more information to understand the factor of biased sex ratio in Neotermes.