Reverse Osmosis (RO) has been used in numerous applications like wastewater treatment and seawater desalination.However,silica and silicate precipitation and organic fouling always act as limiting factors in high-recovery membrane operations.[1] The RO concentrate is generally considered as a waste stream,which leads to a major impact on the ecosystem when discharged.Various methods have been applied for the treatment of RO concentrate such as ion-exchange,electrodialysis,photocatalysis and multistage RO treatment.[2] In this study,a new method was adopted to treat RO concentrate with high salinity,especially silica,containing nutrients and organic compounds by calcium hydroxide pre-treatment followed by ultrafiltration (UF) process,which was shown in Fig.1.The organic containments were totally removed and the silica concentration,as SiO2,could decrease from 120 to 19.5ppm,which was shown in Fig.2.The effects of the calcium hydroxide adding amount on the silica concentration,pH value,conductivity and total dissolved solids of the permeated solution were systematically investigated in this work.There existed almost no fouling in the UF process,resulting from the absorption of the organic containments by calcium hydroxide particles.Fouling propensity was also characterized as the modified fouling index (MFIUF),which was calculated by the equations below.[3] V refers to the filtrate volume and t is the filtration time.The slope of the linear region of t/V vs.V is defined as the MFIUF.The MFIUF had an apparent decrease with the addition of the calcium hydroxide as shown in Fig.3.The result confirm that the combination of the calcium hydroxide pre-treatment and UF process may be a feasible method for the RO concentrate treatment which makes great contributions to the reuse of water resources in industry.