Two new species of damselfishes (Pomacentridae) are described from the Marquesas Islands, Abudefduf conformis, previously identified as A. saxatilis (Linnaeus) or A. vaigiensis (Quoy & Gaimard), and Plectroglyphidodon sagmarius, formerly cited as P. imparipennis (Vaillant & Sauvage). A. conformis is distinct from the Indo-Pacific A. vaigiensis in having modally 13 instead of 12 anal soft rays, usually 22 instead of 21 tubed lateral-line scales, 27-30 instead of 24-28 gill rakers, and in color (edges of scales darker, dark bars narrower, and no yellow dorsally on body). P. sagmarius is distinct from the Indo-Pacific P. imparipennis in having modally 19 instead of 20 pectoral-fin rays, deeper body (2.1-2.35 in SL, compared to 2.3-2.45 in SL) and in color (a black saddle on caudal peduncle and three brownish yellow bars on body, not present in P. imparipennis).