Two new extremely elongate snake eel of the genus Ophichthus are described based on specimens collected from Vietnamese waters. Ophichthuscuulongensis Vo, Hibino & Ho, sp. nov. is distinguished from its congeners by having the dorsal-fin origin slightly behind the pectoral-fin tip, mean vertebral formula 14-63-202, range 12-17/60-64/199-207; teeth on jaws biserial to triserial; dorsal body dark brown, ventral body pale, anal fin initially white but changing to darker towards its tip. Ophichthusnguyenorum Vo, Hibino & Ho, sp. nov. is distinguished by having a snout rather pointed but the occipital convex (duck-shaped); body with numerous longitudinal wrinkles, weak on posterior abdomen; dorsal-fin origin slightly behind the pectoral-fin tip; one row of teeth on the maxilla anteriorly but increasing posteriorly; two rows on the lower jaw; all teeth small; body dark, usually including abdomen; dorsal fin darker with dark margin; anal fin initially pale but changing to darker towards tip; mean vertebral formula: 15-62-192, range 13-17/61-64/190-196. Descriptions of two related species, O.macrochir (Bleeker, 1852) and O.rutidoderma (Bleeker, 1852), are provided with updated morphological data.