Two new species of Pentagonia Bentham (Rubiaceae, Hippotideae) are described and illustrated. Pentagonia tapacula Cornejo is from the pluvial forests of Bajo Calima, Valle del Cauca Department, southwestern Colombia. This new species belongs to a species group of plants with entire leaves that have a tapering, subsessile base, and with a 5-lobed calyx, but differs mainly by its thicker coriaceous leaf blades, obovate stipules, and inflorescences with remarkably elongated and thick peduncles. The second new species is P. clementinensis Cornejo from the wet forests of western Ecuador. This is segregated from P. involucrata C. M. Taylor, which differs sharply by its leaf blades, floral bracts, fruits, and calyces.