Seasonal bycatch composition of the flounder gillnet fishery in the Coquimbo Bay, between October 2006 and November 2007 was analyzed. Landed species were identified and weighted (kg). These data set was used to estimate the relative importance of weight and frequency of occurrence of each species in relation to the total catch. To evaluate the seasonal variation of landed species, we performed cluster analyses (based on frequency of occurrence, mean weight, CPUE), and correspondence analysis (frequency of occurrence; CPUE). Thirty-two species were recorded as bycatch, being the most frequent species, the Chondrichthyan, Callorhinchus callorhynchus, Squatina armata and Mustelus mento. Paralichthys spp., C. callorhynchus, M. mento, Myliobatis chilensis, S. armata and Thyrsites atun, were strongly associated with spring and summer seasons; while Sciaena deliciosa and Merluccius gayi were associated with winter and autumn.