In this study was carried out Middle Black Sea coasts, catch efficiency and length composition of the horsemackerel (Trachurus mediterraneus, S.) has established. 23 tows (net haulings) made in October, a total of 31962 kg and 1389.65 ± 157.75 kg horsemackerel per haul have caught. 5165 of total caught fishes was measured individually and mean length of these fishes was calculated 13.25 ± 0.02 cm. Maximum and minimum lengths of the measured fishes was determined 18.7 cm and 7.1 cm, respectively. The length-weight relationship was determined W= 0.007L3.039(n=696, R=0.98). Total catch and length compositions was examined according to operation time and total catch and mean length values were determined as 6944 kg, 13.44 cm and 12180 kg, 13.22 cm respectively for 7 day time and 7 night operations. Differences between total catch was significant amounts (P0.05). The results show that horse mackerels exhibit various schooling depending on day time and this has a few effect on catch efficiency and length composition of the caught fishes. In light of the these informations, it can be say that horse mackerel fishing with midwater trawls in Black Sea is a successful fishing system in terms of catch efficiency and length composition.