The　effect　of　pre-ozonation　on　fouling　control　is　related　with　ozone-induced　particle　aggregation/destabilization　or　the　structural　changes　of　organic　materials.　To　clarify　the　mechanism　of　pre-ozonation　on　fouling　and　further　optimize　the　use　of　pre-ozonation　in　real　full-scale　UF　membrane　operation　system,　the　actual　sewage　effluent　(SE)　was　filtrated　to　remove　specific　foulants　with　sand　filter,　1.2　mu　m　and　0.45　mu　m　filter.　Then,　UF　membrane　fouling　caused　by　the　remaining　foulants　after　pre-ozonation　was　further　investigated.　As　for　the　SE　pre-filtered　by　sand　filter,　the　results　revealed　that　pre-ozonation　only　slightly　alleviated　the　fouling　of　UF　membrane.　After　pre-oxidation　with　the　ozone　concentration　lower　than　1.53　mgO(3)/mg　TOC,　membrane　flux　dramatically　decreased　in　the　initial　filtration　stage,　accompanying　with　an　obvious　increase　of　the　irreversible　fouling.　With　the　increase　of　ozone　concentration,　the　membrane　flux　was　improved　and　the　irreversible　fouling　was　apparently　decreased.　Besides,　the　retention　of　total　organic　carbon　by　UF　was　strengthened　with　the　increase　of　ozone　concentration.　As　for　the　SE　pre-filtered　by　the　1.2　mu　m　or　0.45　mu　m　filter,　the　effect　of　pre-ozonation　on　fouling　control　was　obvious.　Although　a　slight　increase　of　the　irreversible　fouling　was　also　observed　under　lower　ozone　concentration,　the　total　fouling　and　the　reversible　fouling　presented　a　continuously　decrease　with　the　increase　of　ozone　concentration.　SEM　results　revealed　that　the　fouling　alleviation　by　pre-ozonation　was　related　to　the　aggregation　of　foulants.　Pre-filtration　before　the　hybrid　process　of　pre-ozonation　and　UF　is　helpful　for　fouling　alleviation　and　irreversible　fouling　control　in　processing　the　actual　SE.