Oreophryne rookmaakeri is a species of frog in the family Microhylidae. It is endemic to the island of Flores, Indonesia. The specific name rookmaakeri honours Hendrik Roelof Rookmaaker, a Dutch colonial administrator who was resident on Flores. Common name Flores cross frog has been coined for this species.
One paratype, held at the Bogor Zoology Museum, measures about 26 mm (1.0 in) in snout–vent length. Another paratype at the Museum of Comparative Zoology measures about 30 mm (1.2 in) in snout–vent length.
The type locality is "Rana Mese" in western Flores, although the IUCN Red List of Threatened Species maps it further east on the island.