The mandibularis group of the genus Dolichomitus is reviewed. Three species are recognized, including a new species, Dolichomitus flavicrus sp. n. from Japan. The new species is closely related to Dolichomitus khasianus Gupta & Tikar, in having an entirely blackish underside of the metasoma, but can be separated from the latter by the smooth antero-median part of the first metasomal tergite between the latero-median carinae and a short longitudinal dark stripe on the posterior surface of the fore femur. A key to species of the mandibularis group is provided. Mitochondrial COI gene sequences were generated for D. mandibularis (Uchida) and D. flavicrus sp. n. to permit future comparisons.