Alpheus cedrici sp. n. is described based on two specimens collected under rocks while scuba diving off the coast of Ascension Island, central Atlantic Ocean. The new species belongs to the Alpheus macrocheles (Hailstone, 1835) species complex and appears to be most closely related to the eastern-central Atlantic A. macrocheles, the western Atlantic A. amblyonyx Chace, 1972, and the eastern Pacific A. bellimanus Lockington, 1877 and A. rectus Kim & Abele, 1988. However, it differs from all these species by a combination of morphological characters and by a diagnostic and striking colour pattern. [ABSTRACT FROM AUTHOR]