We describe a new species of Batomys from Mt. Isarog, southern Luzon. Morphological and genetic studies of newly obtained specimens of Batomys granti from the type locality on Mt. Data and other high mountains in the Central Cordillera of northern Luzon, and previously referred specimens from Mt. Isarog on the southern peninsula of Luzon, support the separation of the population from Mt. Isarog as a distinct species that is sister to B. granti and demonstrate the existence of B. granti as a widespread species in the Cordillera. The new species occurs only in montane and mossy forest from 1350 m to 1800 m, and is separated from the nearest known population of B. granti by about 450 km. Limited ecological data indicate that it is a nocturnal herbivore. Recognition of this species raises the number of native murid species on Luzon to 44, and the number of species in the endemic Philippine cloud-rat clade to 18. The new species occurs within a national park that is not currently under threat.