A new species of triplefin, Enneapterygius rubrimarginatus is described on the basis of a single male specimen. The new species is characterized within the genus by having the first dorsal fin higher than the second dorsal fin, 15 anal-fin soft rays, the pectoral-fin with 14 soft rays, 14+17 lateral-line scales, a mandibular pore formula of 3+2+3, the pelvic-fin length about equal to the length of the longest spine of the second dorsal fin, a preanal black blotch present, the anal-fin base with 8 black spots, the pelvic fin pale, and the scales in life with red margins. The new species is compared with similar species of the Enneapterygius tutuilae species group.