Salinity gradient energy (SGE) is a source of renewable energy which utilizes the osmotic pressure difference between two water streams of different salinities. The present paper investigates the effect of environmental water temperature variations on the performance of the pressure retarded osmosis (PRO) process employed to harvest SGE. Using experimental and numerical approaches, the effect of water temperature on water and salt permeabilities as well as membrane structure parameter have been measured using a bench scale system and a commercially available FO membrane. The water and salt permeability coefficients have been found to increase with the water temperature while the membrane structure parameter decreases. This variation in the membrane properties has enhanced the maximum power density of the PRO process by about 90% when the water temperature increases from 10 to 35 °C. New correlations to predict the membrane properties at different temperatures have been developed and validated against the tested membrane as well as other membrane properties data available in the literature. This study highlights the importance of understanding the effect of water stream temperature to accurately predict the performance of PRO process that is utilized for harvesting the salinity gradient energy.