It is endemic to Malaysia and only known from its type locality, a small cave near the top of Gunung Kajang (=Mount Kajang), on Tioman Island,[1][3] a small island located 32 km off the east coast of Peninsular Malaysia.

The type series consists of two adult males measuring 35–36 mm (1.4–1.4 in) in snout–vent length—a relatively large size for the genus Leptolalax (now Leptobrachella).

There is also an earlier collection of tadpoles from a lower altitude on the same mountain that are morphologically similar to the ones at the type locality but that differ in colouration; they might represent another species.

[2] Tioman Island was connected with Peninsular Malaysia as late as the Pleistocene.

However, Grismer et al. considered it unlikely that Leptolalax kajangensis could have dispersed over flat, low-lying landscape to Gunung Kajang; instead, they suggest that the presence of this species on Tioman Island represents much older vicariance, that is, the species (or its ancestors) would have reached Tioman Island when it was still part of a larger mountainous landscape.