Effect of arboreal activity on nesting site selection in Apodemus argenteus was examined by using nest boxes, a footprint recording technique, and live-trapping. Although the breeding season of A. argenteus was from April to September, the use of nest boxes placed on the trunks of trees was observed only from late July to September when use of the arboreal habitat by A. argenteus became active. Nesting site selection of A. argenteus was closely associated with their spatial activity.