Poor selectivity of conventional trawl codends has recently been a serious concern in Turkish fisheries. Modification of the codends to reduce the capture of juvenile fish has been one of the management tools for sustainable fisheries. This study investigates effect of square mesh escape window installation on selectivity of bottom trawl codends for red mullet (Mullus barbatus), annular sea bream (Diplodus annularis) and common pandora (Pagellus erythrinus) in the Aegean Sea. Codend mesh selectivity experiments were carried out using 40 mm nominal diamond mesh PE codend with a square mesh escape window inserted in the forward part of the top panel. The experiments were carried out in lzmir Bay in the eastern Aegean Sea between 24(th) June and 31(st) July 2002 on board RN "Egesuf". A total of 9 valid hauls were made by using hooped covered codend method. Selectivity parameters were obtained by using logistic equation with the maximum likelihood method.