Preventing biofouling of reverse osmosis (RO) membranes is the major issue in seawater (SW) RO desalination. Ultrafiltration (UF) has shown its efficiency when used as a pretreatment step but it is not sufficiently effective in removing dissolved organic carbon (DOC), which is a source of nutrients responsible for biofouling. This study focuses on adsorption by granular activated carbon (GAC) as a step to remove DOC before UF. It provides in the case of real SW, a lab-scale demonstration, of the interest of this coupled pretreatment for water quality and UF performance. GAC filtration enabled the Silt Density Index and turbidity to be strongly reduced and removed around 70% of DOC and around 90% of colloidal transparent exopolymer particles in SW. GAC filtration prevented fouling of 200 kDa and 50 kDa membranes. The 200 kDa membrane did not remove any DOC while the 50 kDa removed about 20%. For SW, UF fouling is mostly reversible and is attributed to cake deposit on the membrane surface. Fouling is much lower and mostly irreversible when GAC pretreated SW is ultrafiltrated. The combination of GAC and UF showed great promise for reducing the RO fouling potential of SW.