Small rodents living in forests use various spaces on trees for arboreal activities such as daily rest, hibernation, foraging, sheltering, roosting, and nesting. To investigate the differences in arboreal activity between two sympatric cavity-nesting rodents, Glirulus japonicus and Apodemus argenteus, we compared the frequencies of nest box use by these species at three different heights, and surveyed tree cavities. We observed that G. japonicus used nest boxes mounted at a relatively greater height most frequently, whereas A. argenteus used boxes placed at lower heights. Glirulus japonicus used all nest boxes for resting, while A. argenteus used most nest boxes for food hoarding. The tree cavities that were used by G. japonicus were located significantly higher than those used by A. argenteus. In a multinomial logistic regression analysis, height at which a cavity was located was identified as factor affecting frequency of cavity use.