Microhyla borneensis (junior synonym Microhyla nepenthicola), also known as the Mantang narrow-mouthed frog, is a species of microhylid frog found in the Matang Range in Sarawak, Borneo. It was once the smallest known frog from the Old World (the current record holder is Paedophryne amauensis from New Guinea).

Adult males of this species have a snout-vent length (SVL) of 10.6–12.8 mm.

Tadpoles measure just 3 mm. It is one of 30 species in the genus Microhyla, 5 others of which live in Borneo. It is endemic to Borneo. Its natural habitats are subtropical or tropical moist lowland forests and intermittent freshwater marshes. The International Union for Conservation of Nature does not consider it threatened.