A new species of deepwater cardinalfish, Epigonus okamotoi from off southwestern New Britain, Papua New Guinea, is described on the basis of a single specimen collected with a trawl in 315-624 m depth in Ainto Bay. The new species is characterised by the following characters: dorsal-fin rays VII+I, 9; pectoral-fin rays 15; total gill rakers 22; pyloric caeca 4; pored lateral-line scales 47+4; scales below lateral line 8; vertebrae 10+15; opercular spine present; maxillary mustache-like process absent; ribs absent on last abdominal vertebra; upper margin of pectoral-fin base on level or upper margin of pupil; proximal radial of first anal-fin pterygiophore slender; mouth cavity light grey. The new species is compared with other species in the genus.