The essential point for a successful seawater reverse osmosis (SWRO) plant is pretreatment that provides consistent and high-quality feed to SWRO membranes. Advances in membrane technology and increasing requirements on water quality have stimulated the use of ultrafiltration (UF) for SWRO pretreatment. In this study, inside-out (module A) and outside-in (module B) hollow fiber UF modules were adopted as the pretreatment prior to SWRO desalination at Qingdao Jiaozliou Bay, the Yellow Sea of China. The performances of the two modules were compared to operation parameters and permeate qualities. Based on the flux data, TMP and permeability, the outside-in UF module consistently performed better with an air enhanced backwash than the inside-out one using a chemical enhanced backwash, which was not particularly efficient for the outside-in module. As to permeate quality, both modules met the demand of the SWRO feed.