A new species of the genus Ampelisca Krøyer, 1842 is described and illustrated in detail. The specimens were collected from soft bottom at 15 m depth in the northern coast of Santa Margarita Island, Mexico. Ampelisca capetilloi sp. nov. is characterized by: head as long as pereonite 1-2 combined; mandible with 8 rakers; maxilla 1 palp article 2 expanded distally; gnathopod 1 propodus anterior margin with 7 distal setae; pereopod 7 basis reaching middle portion of merus, posterodistal lobe of merus large, extending one-third of carpus; pleonite 3 dorsal margin smooth; urosomite 1 slightly sinuous dorsally; telson bilobate, each lobe with 3 dorsal setae. The new species is similar to Ampelisca mexicana Barnard, 1954 and A. pugetica Stimpson, 1864, but can be easily recognized with the identification key included herein. A checklist for Ampelisca species documented from the Eastern Tropical Pacific, including their geographic distribution, habitat, and depth range, is provided.