Callionymus vietnamensis sp. nov. from Vietnam, South China Sea, is described on the basis of five specimens collected with a trawl in 60-68 m depth southeast of the Côn Đảo Islands. The new species is characterised within the subgenus Callionymus (Calliurichthys) Jordan & Fowler 1903 by 4 dorsal-fin spines, 9 unbranched soft rays in second dorsal fin (the last divided at base), 8 unbranched soft rays in anal fin (the last divided at base), 8-13 antrorse serrae dorsally on the preopercular spine (additional to the main tip and a strong antrorse spine at the base), caudal-fin length in the male 0.8-0.9 in SL, in the female 1.1-1.2 in SL, preorbital length 2.1-2.5 in head, first to third spines of first dorsal fin filamentous in both sexes, second spine longer than third (male) or shorter than third (female), first dorsal fin without an ocellus in both sexes, distal four-fifths (male) or three-fifths (female) of anal fin black, thorax with a small heart-shaped dark blotch in male in male, posteriorly surrounded by ocellate lines which are reaching on membrane connecting pelvic fin with pectoral-fin base. The new species is compared with similar species. The subgenus Callionymus (Calliurichthys) Jordan & Fowler 1903 is reviewed, and a key to the species in this subgenus is presented.