pleuronectiformes is one of the most important fishes in the Persian Gulf and Oman sea. Which has been studied in the project of “stock assessment of demersal resources by swept-area method. A research cruise were conducted by R/V Ferdows-1 in the Oman Sea (Coastal waters of Sistan-O-Baluchistan Province) by swept area method in 2013. The area chosen for the study was from Meidani (58° 55' E) to Gwatre Bay (61° 30' E) having depths of 10 to 100m.The studied area was divided into 5 subregions (A,B,C,D&E). Each region was divided into 4-depth stratum: 10-20, 20-30, 30-50, and 50-100 meters. After hauling the samples were identified, weighted and also some biological measurements were done. The flat fish biomass and catch per unit area (CPUA) to separate the 5 regions (the study area) in the region B Maximum value of 15.2 tons and the region E minimum value of 9/0 tons respectively. The maximum biomass for the stratum of 10-20 m and 22.9 tons and while the minimum was found in the depth of 30-50 of 0.2 tons respectively. Significant deference about mutual effect and stratum-depth was seen among studied pleuronectiformes.