Developmental systems of Reticulitermes and many other termite taxa are characterized by possessing two different developmental pathways, nymph-alate line and worker line. It is generally thought that extrinsic factors, such as pheromones, determine which line a young larva differentiates into. In Reticulitermes, two types of neotenic reproductives, nymphoids and ergatoids, emerge from the nymph-alate and the worker lines, respectively. Recently, we carried out crossing experiments using male and female nymphoids and ergatoids of R. speratus (Kolbe) (Hayashi et al., in prep.). Crossing of different combinations of castes of the parents resulted in significantly different sex and caste ratios of their offspring. Based on the results, we proposed a hypothetical genetic model of the caste determination (Hayashi et al., in prep.). In this study we carried out the crossing experiments with the same sex/caste combinations using R. kanmonensis Takematsu. We examined sexes and castes of the offspring reared under a controlled environmental condition. Offspring of R. kanmonensis differentiated into nymphs and workers in a similar ratio to R. speratus, and did not significantly different from the expected value of the model. These results suggest that a common intrinsic mechanism determines the nymph/worker castes in both species.