A new species of the genus Spinaethorax Papáč & Palacios-Vargas, 2016, recently erected for two cave species of Mexico, is described from a Vietnamese cave. It differs from the Mexican species most noticeably by the dorsal chaetotaxy of the head (number and morphology of chaetae), the shape of S-chaetae on the third antennomere, the dorsal chaetotaxy of the abdomen and the chaetotaxy of the dens. The pattern of special τ-chaetae is described for the first time in the genus. The affinities between Spinaethorax and the other genera of Neelipleona are discussed. Spinaethorax is probably closely related to Neelus Folsom, 1896. A table of the differential characters is provided for the three known species of Spinaethorax. Spinaethorax appears to be restricted to caves, but its presence in Vietnam indicates that this genus has a much larger distribution than previously recognized.