Ultrafiltration　(UF)　was　implemented　as　a　process　upgrade　in　a　full-scale　drinking　water　treatment　plant　(DWTP)　with　a　scale　of　100,000　m(3).d(-1),　and　the　performance　was　systematically　investigated　over　seven　years　of　operation.　The　results　showed　that　the　UF　system　exhibited　excellent　rejection　of　particles　and　improved　the　removals　of　organics　by　9.0-14.7%.　The　annual　average　UF　flux　decreased　from　28.37　to　16.51　L.m(-2).h(-1),　and　it　was　necessary　to　employ　various　cleaning　approaches　at　an　increasing　frequency　for　maintaining　stable　operation.　Compared　to　the　initial　scenario,　the　total　cost　per　m(3)　of　water　for　the　UF　system　after　7-year　operation　increased　by　55%.　The　cost　of　membrane　replacement,　energy,　waste　water　and　chemicals　played　a　decisive　role　on　operating　cost　in　the　lifecycle　of　the　UF　system.　The　content　of　cations　(i.e.,　Mg,　Al,　Si,　Ca,　Mn　and　Fe),　biological　metabolites　and　organic　substances　in　the　cake　layer　increased　significantly　during　long-term　UF　filtration,　which　not　only　aggravated　membrane　fouling　but　also　affected　the　organic　composition　of　the　drinking　water.　The　excellent　integrity　of　the　UF　membrane　during　the　7-year　operation　was　sufficient　to　prevent　breakthrough　of　the　organic　substances　from　metabolic　activity　of　microorganisms　and　to　ensure　biological　safety　of　the　permeate.