An energy generated by mixing two solutions with different salinities is termed salinity gradient energy (SGE). This energy could be used for electricity production by some methods (e.g. Reverse Electro-Dialysis (RED); Pressure Retarded Osmosis (PRO) … etc.). Estuaries or Delta, as zones for mixing of freshwater from rivers and saltwater from the sea, have a large power potential of this renewable energy. The Sebou estuary in Morocco is being used in a trial of osmotic power technology using Pressure Retarded Osmosis (PRO). Currently, there is no information available about the potential energy production from salinity gradient in the Sebou estuary. PRO potential in the Sebou estuary is the main objective of this study. The highest mixing energy is 0.712kWh/m3 in March and October, when ф = 0.5 and T = 298 K (temperature). Based on the river estuary flow, PRO can generate 80.33 MW-164 MW of power. Regarding the ecological flow criteria, PRO power generation’s installed power potential ranges from 85 to 158 MW. When the design flow, power factor and installed capacity are 25.78 m3/s, 0.8 MW/(m3/s) and 21.37 MW, respectively, annual electricity energy generation is calculated as 123.42GWh/y. The results show that the pressure retarded osmosis power plant is technically reasonable for the site.