Positional behavior of Japanese giant flying squirrels (Petaurista leucogenys) was studied based on 3,318 positional bouts and 2,687 instantaneous samples. Resting, feeding and foraging, locomotion, and grooming were the most common behaviors. The most common locomotor behaviors were leaping, scrambling, walking, bounding, vertical bounding, and gliding. The most common postural behaviors were quadrupedal squatting, hind-limb squatting, vertical clinging, clinging, and crouching. Compared with smaller tree squirrels, Sciurus igniventris and Microsciurus flaviventer, P. leucogenys exhibited a higher frequency of “scrambling” for foraging among terminal branches. The tree squirrels foraged on terminals but fed on larger branches. They also foraged and fed more on vertical surfaces. P. leucogenys spent the most time on small supports, whereas the smallest squirrel (M. flaviventer) spent most on the largest supports.