Ansonia hanitschi is a highland stream toad. Calling males sit on low vegetation and saplings close to the river at night. 

Adult males 20–30 mm snout-vent length, females up to 35 mm. 

Ansonia hanitschi tadpoles are the largest (33 mm total length) Ansonia tadpoles known from Borneo. In close up they have a salt-and-pepper coloration. When approaching metamorphosis, color patterns of the toadlet form in the tadpole.

Tadpoles of this species adhere to rocks in torrential water by means of their strong oral sucker. The tail is strong and the tail fin reduced; at it's end with a small sharp flagellum. They are commonly found on vertical smooth rock faces in foaming water, but may crawl on horizontal sections as well, especially at night. We have seen them even crawl out of the water and graze on algae in the splash zone.