Branchiosyllis differs from other syllid genera by possessing claw-shaped falcigers. There are 18 valid species in the genus, but only five have been reported from Mexico: B. diazi Rioja, 1958, B. exilis (Gravier 1900), B. oculata Ehlers, 1887, B. pacifica Rioja, 1941, and B. salazari Ruiz-Ramirez & Harris, 2008. During diverse sampling campaigns along Western Mexico, specimens of two undescribed species were found. Branchiosyllis sanmartini, new species, was collected in La Paz Bay, in rocky bottoms. Its body is subcylindrical anteriorly, depressed in median and posterior regions, and with segments that are strongly pigmented black on the dorsal side. The palps are divided by a dorsal groove appearing bilobed; without branchiae; anterior parapodia with bidentate falcigers in dorsal position, ventral ones unidentate, in median parapodia all falcigers unidentate, posterior parapodia with claw-shaped falcigers. This species differs from all others in the genus due to its color pattern, the shape and distribution of falcigers along the body, the subcylindrical shape of the anterior end, and the dorsoventrally flattened shape of the middle and posterior region. Branchiosyllis riojai, new species, was collected in Phragmatopoma sp. beds in Manzanillo, Colima, and María Madre Island, Nayarit, among algae and sponges. This species has a cylindrical body, without color pattern; branchiae absent; bidentate dorsal falcigers on anterior and median parapodia; claw-shaped falcigers from median chaetigers. Branchiosyllis riojai has been reported for the Mexican Pacific as B. exilis (Gravier 1900), described from the Red Sea, but it differs from the nominal species in falciger distribution along the body, shape of antennae, tentacular cirri and dorsal cirri, as well as in the number and shape of aciculae. A key to all species of Branchiosyllis from Mexican waters is included.