A new species of forest frog of the genus Platymantis is described from an elevation of 140 m in the Taft Forest Reserve in eastern Samar Island, Philippines. It is assigned to the Platymantis guentheri Species Group, a group of primarily arboreal species, and is distinguished from these and other congeners by features of its external morphology and its preferred terrestrial, limestone microhabitat. Several striking morphological characters include a large body (34.2–39.1 mm SVL for 9 males and 44.3–49.8 mm SVL for 9 females), greatly expanded finger and toe discs, large eyes, spotted flanks, and sparsely-distributed, salmon-colored dorsal dermal tubercles. The new species represents the second largest Philippine Platymantis, the third terrestrial species in the P. guentheri Group, and the only known species of Platymantis from the Mindanao Faunal Region with a preference for forested, karst habitats.