A seawater reverse osmosis plant of 1800 m3/day capacity is part of the 6300m3/day capacity nuclear desalination demonstration project at Kalpakkam. The plant was commissioned in October 2002 and is in continuous operation. This paper deals with types of foulants, membrane cleaning procedures and the improvement in the reverse osmosis system after cleaning. This paper also describes the analysis of foulants, which may consist of adsorbed organic compounds, particulate matter, micro-organisms and metallic oxides, and describes the chemical cleaning procedure to be adopted, which is specific the seawater used because the membrane foulants are very specific with respect to the seawater constituents. The cleaning of the membranes in the Kalpakkam nuclear desalination plant was taken up because the quality of the permeate had deteriorated and the differential pressure across the membrane had gone up. This paper essentially deals with the selection of cleaning chemicals, the experience gained with the cleaning procedure adopted and the effects of cleaning on the membrane system. Copyright © 2006 Inderscience Enterprises Ltd.