Square mesh windows (SMWs) with 75 (75SMW; 37.5 mm bar length) and 90 mm (90SMW; 45 mm bar length) nominal mesh size were tested for determining size selectivity in dhow prawn fisheries of the Persian Gulf (Hormuzgan province). Fishing trials were conducted on the commercial fishing grounds of Hormuzgan province of the northern Persian Gulf by commercial dhow trawler. Covered codend methods were utilized for collecting data during October and November 2012. Totally 21 and 16 valid hauls were performed with 75SMW and 90SMW, respectively. The mean L50 values of 75SMW and 90SMW were found as 3.6 +/- 0.03 and 3.7 +/- 0.02 cm carapace length for banana prawn (Penaeus merguiensis), 2.9 +/- 0.03 cm and 2.9 +/- 0.05 cm carapace length for Jinga shrimp (Metapenaeus affinis), 8.0 +/- 0.08 cm and 9.5 +/- 0.11 cm fork length for Indian ilisha (Ilisha melastoma), and 8.1 +/- 0.04 and 8.4 +/- 0.03 cm fork length of sulphur goatfish (Upeneus sulphurous), respectively. This study clearly shows that there is not any notable different in size selectivity of square mesh windows with different mesh sizes for investigated species. Future studies on different by -catch reduction methods such as full square mesh codends or grids should improve size selectivity of the species and efforts to reduce by -catch in this fishing system.