In the present study, size selectivity of a commercial (300 MC) and a larger square mesh top panel (LSMTPC) codend for blue whiting (Micromesistius poutassou) were tested on a commercial trawl net in the international waters between Turkey and Greece. Trawling, performed during daylight was carried out at depths ranging from 124 to 230 m, and towing speed changed between 2.2 and 2.3 knots for a 13-day sea trial in August 2005. Selectivity data were obtained by using the covered codend technique. Selection parameters were estimated by fitting a logistic equation using the maximum likelihood method. The results show that mean L(50) values of 16.98 (s.e. 0.22) and 22.84 (s.e. 0.51) cm were estimated for 300 MC and LSMTPC, respectively. These values show that the LSMTPC codend has higher L(50) values than the 300 MC codend. In view of the length value of blue whiting at first maturity (15 to 18 cm), mean L(50) value of LSMTPC codend is remarkably higher than 300 MC codend.