A new frog, Philautus griet sp. nov., is described from Munnar in the Western Ghats of India. Molecular phylogenetic analyses of a 548 bp fragment of the mitochondrial 16S rRNA-gene confirm its placement in the genus Philautus (Anura, Ranidae, Rhacophorinae). In its small size, general brown coloration, and reduced webbing on toes, the new species is similar to Philautus bombayensis and Philautus tinniens. However, relative to P. griet, P. bombayensis differs by the invariable presence of greyish-black and yellow spots in the groin and on the inside of the thighs, and P. tinniens can be distinguished by the dark side of the head and the yellow inner fingers and toes. Phylogenetic analyses of Indian and Sri Lankan Philautus have identified Philautus charius as the sister taxon of P. griet. However, the latter can be readily distinguished by its smaller adult size (20.7–22.1 mm, N = 5, vs. 27.5–30.9 mm, N = 10, in P. charius) and lack of black coloration with yellow spots on the posterior surface of the thighs. The 30 km wide Palghat Gap, dividing the Western Ghats into northern and southern components, may have played a role in the vicariant isolation of these species.