These experiments were conducted with secondary effluent from the terminal plant at Osaka, Japan, in order to determine the potential of the sponge ball cleaning system as an advanced reverse osmosis membrane cleaning technique. It was confirmed that sandfiltration of the feed as a method for reverse osmosis pretreatment and the use of chemical cleaning reagents to restore flux levels were unnecessary, when sponge ball cleaning was used. As a result, the product water flux was maintained at 0.65 ∼ 0.75m 3/m 2 day at 25°C and membrane rejection was more stable. No damage to the membrane, which would mean a decline of rejection ability, was recognized by scrubbing of the membrane surface by sponge rubber balls. It was confirmed that tight membranes were more suitable than loose ones because firstly it was easier to remove membrane fouling, secondly the product flux was nearly equal, and finally the product water was of better quality.