Proper pre-treatment is the most critical factor for successful long-term performance of reverse osmosis seawater desalination plant. The objective of the study was to assess the potential of ultrafiltration (UF) pre-treatment prior to reverse osmosis (RO) for desalting seawater with high-fouling tendency. A UF pilot plant equipped with an Aquasource membrane directly operated on Gibraltar surface seawater in dead-end mode. The competitiveness of UF pretreatment towards conventional pre-treatment was assessed by looking at the impact on RO hydraulic performances. The study showed that ultrafiltration provided permeate water with high and constant quality resulting in a higher reliability of the RO process than with a conventional pre-treatment. The combination of UF with a pre-coagulation at low dose helped in controlling the UF membrane fouling and providing filtered water in steady state conditions. The performance of RO membranes downstream UF exceeded the usual operating conditions encountered in seawater desalination. The combined effect of higher recovery and higher flux rate promises to significantly reduce the RO plant costs.