Abstract Seawater desalination of interest is rising to overcome water scarcity. Especially, desalination using RO membranes is increasingly being used for production of drinking water for brackish and/or seawater. SWRO has operational problems that can be caused by various membranes fouling including particulate, inorganic, organic and bio-fouling. Membrane-based pretreatment for particle fouling and the integrated membrane systems with MF, NF, and RO were recently introduced to SWRO. However, little information is known for SWRO processes combined with various pretreatments. Eff ects of various pretreatments on performance of SWRO were evaluated in this study. The RO membrane flux was substantially improved by nanofi ltration pretreatment resulting in the highest flux regardless of pretreatment for particle fouling. However, the water flux with the other pretreatments including MF with antiscalant addition is severely decreased during a few hours. The microfi ltration pretreatment showed greater flux than the coagulation pretreated water. Coagulation pretreated waters was observed to have relatively high MFI resulting from residuals such as flocs and colloidal particles. The correlations of turbidity, normalized flux ratio and MFI were substantial indicating feasibility of the use of MFI for particle fouling index. The conductivity removal was signifi cant, but the cation removal was not great by NF. The results of the inorganic ions removal indicate that pretreatment process aff ects properties of feed water to RO. The application of inorganic scaling control pretreatment has shown no influence on the crystal structure but there were changes in the intensity related with calcium scale inhibition in the XRD analyses.