Persian Gulf is one of the most important and most various aquatic ecosystems in the world due to its location in tropical area. Shrimp trawling is one of the fishing methods in such ecosystem that have high range of by-catch. This study aimed to achieve the percentage of less length frequency of LM50 in three commercially species, namely Pomadasys kaakan, Otolithes rubber and Pampus argenteus in Hormozgan shrimp fishing grounds using shrimp trawl fishery. Samples were taken by shrimp trawl with 2 cm stretched mesh size in codend. The entire operation was conducted by 16 trawling. The largest and smallest individuals trapped by trawling was 520 and 120, 360 and 240 mm total length and 259 and 109 mm fork length for Pomadasys kaakan, Otolithes rubber and Pampus argenteus, respectively. Analysis of length frequencies showed that for P.kaakan 92.85%, P.argenteus 80.39% and O.rubber 73.33 % of total length and fork length of all obtained samples, were shorter than the length were cited in references for LM50 of species. It is suggested to use by-catch reduction device to prevent damage on the stock of these three species in Persian Gulf.