A new species of the hylid frog genus Osteocephalus from the upper Amazon B
asin of Ecuador and Peru is described. It most closely resembles O. planice
ps, but it differs in the absence of pale stripes on the heels and above th
e vent, in being smaller, and lacking brown spots on the flanks. The new sp
ecies, O. yasuni, is unique within Osteocephalus in having extensive yellow
ventral coloration.