Pressure retarded osmosis is a membrane based technology that produces osmotic power as a sustainable energy by using salt and fresh waters. Pretreatment reduces membrane fouling as the main challenge in Pressure Retarded Osmosis (PRO). In this research, ultrafiltration and a sand filter were used for removing total organic carbon (TOC), turbidity, and hardness. In trials, efficiency and required power of the two methods were compared. Highest removal efficiency of turbidity occurred at 3.72 NTU and was 100% and 68.6% for ultrafiltration and the multimedia sand filter, respectively. Maximum TOC removal in ultrafiltration multimedia sand filter was 41% and 1.5% at 6.62 mg/L TOC initial concentration respectively. In all experiments, it was indicated that ultrafiltration had better removal efficiency and consequently more potential for osmotic power generation process improvement.