Investigation on the catch composition, catch per unit effort, and economic analysis of four different mesh sizes of bottom gill nets with the same hanging ratio used in the Atatürk Dam Lake. Four different mesh size of bottom gillnets (110 mm, 120 mm, 130 mm and 140 mm) with same hanging ratio were used to determine their catch composition and the catch per unit effort (CPUE). This research was carried out in fishing zone of the Bozova Town, between 01.08-31.12.2003. During the study 7 fish species belong to 4 different family were caught as follows; Cyprinus carpio (Linnaeus, 1758) (Cyprinidae), Carasobarbus luteus (Heckel, 1843) (Cyprinidae), Capoeta trutta (Heckel, 1843) (Cyprinidae), Torgrypus (Heckel, 1843) (Cyprinidae), Silurus triostegus (Heckel, 1843) (Siluridae), Mastacembelus simack (Banks ve Solander, 1794) (Mastecembalidae) and Oncorhynchus mykiss, (Walbaum, 1792) (Salmonidea). Total catch record in number was 791 fish and in weight was 789 kg. The highest mean CPUE values in gill nets for different mesh size by species were resulted as follows; Cyprinus carpio; 0.402 ± 0.2865 kg/hour with 100 mm mesh size, Carasobarbus luteus; 0.765 ± 0.6657 kg/hourwith 140 mm mesh size, Torgrypus; 0.840 ± 0.5469 kg/hour with 140 mm mesh size and Capoete tnitta; 0.181 ± 0.1012 kg/hourwith 140 mm mesh size. To cover the fishing cost, the gill nets with 110,120 and 130 mm mesh size should be used at least 5 times, whereas the gill net with 140 mm mesh size should be used at least 3 times.