Larval traits provide useful taxonomic characters. The only morphological synapomorphy that separates Scinax species from Ololygon species comes from larvae. However, tadpoles of Ololygon and Scinax remain undescribed; furthermore, there is a lack of information regarding their internal oral cavities. Herein, we describe the tadpole of Scinax cardosoi and its internal oral morphology. Overall, the body is triangular and depressed in lateral view and oval in dorsal view, the dorsal fin is slightly higher than the lower fin, and the tooth row formula is 2(1,2)/3. The tadpole of S. cardosoi can be distinguished from tadpoles of Ololygon and Scinax by its oral disc morphology and oral papillae arrangement. The position of the larval vent tube, as well as some adult features, suggest a close relationship between S. cardosoi and species of Ololygon, leading us to transfer the species from Scinax to Ololygon.