The crustacean fauna associated with Mytilus galloprovincialis and Mytilaster minimus (Mollusca, Bivalvia) beds from Izmir Bay was investigated spatially in autumn 2014. Samples were collected by means of a quadrate.sampler covering 400 cm(2) at four intertidal stations from the inner (3 stations) and outer (a single station) parts of the bay. A total of 831 individuals belonging to 16 species of crustaceans, were collected and identified. Among these, the isopod Paradella dianae was the most dominant species represented with 227 individuals. Paradella dianae and the amphipod Hyale crassipes were the most frequent crustacean species on the mussel beds with 58.33% occurrence. The maximum crustacean biomass (306.29 g/m(2)) was calculated at station 4. The amphipods Stenothoe gallensis and Elasmopus pectenicrtd, and the isopod P. dianae were the alien crustaceans encountered in the present study.