We describe a new species, Hyphessobrycon sebastiani, from the San Juan River drainage of the Pacific versant of Colombia. This new species of Hyphessobrycon is distinguished from all congeners that share two humeral spots and no caudal blotch by having: five unbranched and 25 to 28 branched anal–fin rays; 12–13 branched pectoral–fin rays; 35–37 scales in the longitudinal series; eight scales between the lateral line and the dorsal–fin origin; 12–13 predorsal scales; 13–18 pored lateral–line scales and three pairs of large bony hooks on anal fin of mature males.