The present study was carried out in order to determine the molluscan species distributed in Kusadasi Bay. The investigated material was collected from different biotopes at 11 stations at varying depths between 0 and 180 m; it was sampled in the years 2000 and 2005 by using a van Veen grab and a dredge, and randomly by snorkeling. The study resulted in 134 molluscan species determined in Kusadasi Bay. Among them, Septifer cumingii Recluz, 1849 and Mytilaster solidus Monterosato, 1883 are new records for the Aegean coast of Turkey. Of the identified species, Bittium latreillii (Payraudeau, 1826) (1401 ind.), Musculus costulatus (Risso, 1826) (773 ind.), Bittium reticulatum (da Costa, 1778) (330 ind.), Columbella rustica (Linnaeus, 1758) (140 ind.), Rissoa similis Scacchi, 1836 (81 ind.), and Tricolia pullus pullus (Linnaeus, 1758) (59 ind.) are widely distributed in the bay, whereas the other species have a restricted distribution. Some ecological characteristics with distributional features of the identified species are also given in the present study.