Ansonia leptopus is a common lowland stream toad. The individuals depicted on this page are from Gunung Santubong, Sarawak. Calling males sit on boulders and rocks on river banks at night. Adult males are 30–40 mm in snout-vent length, females are up to 65 mm.
Ansonia leptopus tadpoles are very distinct. Black markings on a light background make the tadpole of this species unique. Only Ansonia longidigita larvae are to some degree similar. Tadpoles of this species are small (< 20 mm). They are associated with submerged vegetation or leaf litter, and on rocks in stream sections with slow current. The oral sucker is less well-developed than in other Ansonia larvae.