Polychaete samples were taken by SCUBA divers in six stations on the Cabo Pulmo-Los Frailes coral reef barriers, in dephts from 4 to 17 m, on dead fragments of coral Pocillopora verrucosa. 556 specimens were collected belonging to 82 species, 61 genera and 21 families. A check-list and brief diagnosis of species with new records for Gulf of California are given. The family Syllidae has the largest number of species (14), followed by Serpulidae (11) and Eunicidae (9). The most abundant species were the sabellariid Idanthyrsus pennatus with 162 specimens (29%), the eunicid Eunice antennata with 47 (9%), and the syllid Trypanosyllis (Trypanedenta) taeniaformis with 21 (4%). Five taxa are new records for Mexico. Range extensions: one from California, Hydroides gracilis; three from the Western Pacific, Typosyllis cf. taprobanensis, Nereis jacksoni and Placostegus sp.; and one from the South Atlantic Ocean, Proscoloplos sp.