Tarsius pumilus eat primarily arthropods with heavily keratinized exoskeletons. Prey are caught by a sudden leap and chewed with a side to side motion of the jaw. Tarsius pumilus drink water by lapping. One at the beginning of the rainy season and the other at the end of the rainy season. Births occur in May and November- December.
Young females remain with their parents until adulthood while young males leave as juveniles.
In the dense vegetation of their habitat, T. pumilus spend most of the day sleeping on vertical branches or possibly in hollow trees. When clinging to a vertical branch, the tail of Tarsius pumilus is often braced against the vertical support and functions in supporting the body. When sleeping, the heads of T. pumilus tend to drop downward between the shoulders. If disturbed while resting they may move up and down the vertical support with the face presented towards the enemy, mouth open, and teeth barred. When waking, the ears of T. pumilus are furled or crinkled continuously.