During three cruises of the former Soviet research vessels R/V “Akademik Petrovsky” (Cruise AP-14) and R/V “Odissey” (Cruises 0–33, 0–34) to the Western Indian Ocean, 120 species of the superfamilies Portunoidea and Xanthoidea were collected. Species of the following families are identified in the present study: Portunidae (37 species), Xanthidae (64 species), Trapeziidae (12 species), Carpiliidae (1 species), Menippidae (4 species), and Xanthoidea incertae sedis (2 species). The geographical range of 17 portunid and xanthoid species is substantially extended, one species,Charybdis hawaiensisEdmondson 1954 was previously known only from the Pacific and is recorded for the first time from the Indian Ocean. The recent synonymy and updated distribution records are given for all species examined, and zoogeography as well as habitat selection of the more common species are discussed.