To investigate the effect of twine thickness on the selectivity of multifilament gillnet targeting bogue, Boops boops L., four different stations were sampled between March and November 2008 in the North Aegean Sea. Gillnets with 22, 23, and 25 mm nominal mesh size (bar length) each having two different twine thicknesses (approximately 0.45 mm and 0.54 mm empty set) were applied for this purpose. The deviances from the SELECT method revealed that lognormal models provided the best fits for both of the twine thicknesses. Results from the two-way ANOVA analyses revealed that the mean total lengths increased with the mesh size (F = 87.36; df = 2; P < 0.0001) and decreased with the twine thickness (F = 46.12; df = 1; P < 0.0001). The 22 mm mesh size net (0.45 mm empty set) captured significantly larger fish than the 23 mm mesh size net (0.54 mm empty set), probably due to the higher elasticity and flexibility of the thinner twine. Thus, fisheries' managers should take into consideration twine thickness while advising mesh size regulations in gillnet fisheries.