Annular sea bream (Diplodus annularis L., 1758) is one of the most abundant species among demersal fishes in the Aegean Sea. The object of this study was to determine the selectivity parameters of 52-54-56 mm stretched mesh size monofilament gillnets used for catching the annular sea bream in the İzmir Bay in the Eastern Aegean Sea. Selectivity curves were determined using Sechin method, which estimates probability of fish retention as a function of morphometric features of the body between head and maximum girth of fish. The estimated selectivity curves corresponded well with size frequencies obtained from each mesh size. The optimum catch length of the monofilament gillnets with 52-54-56 mm mesh size were calculated as 12.5 cm-13.5 cm and 14 cm, respectively. The result of the study showed that using monofilament gillnets with 52 mm mesh size could have increasing fishing pressure on the D. annularis population in İzmir Bay, but monofilament gillnets with 54 and 56 mm mesh sizes would have not such an effect. For sustainable D. annularis fisheries, it can be suggested that monofilament gillnet with greater than 52 mm stretched mesh size should be used in İzmir Bay