The mechanism for removal of phenol by zero-valent iron (ZVI) was quantitatively evaluated in the presence of dissolved oxygen by varying the pH from 2 to 8.1 (natural). The measurement of OH radical concentration suggests that the removal of phenol by ZVI was occurred due to the decomposition by the Fenton reaction besides the adsorption/precipitation to the iron surface. From the measurements of dissolved organic carbon (DOC) in the filtrate with the 0.45 mu m syringe filter and the solution obtained from acidification of suspended precipitates, the roles of decomposition by the Fenton reaction and adsorption/precipitation were separately evaluated. At solution pH 3,91% of phenol removal was achieved and 24% of TOC (total organic carbon) decreased. The contribution of the Fenton reaction was found to be 77% of overall TOC reduction. When the pH values were 4 and 5, the overall TOC removal was found to be mainly due to the adsorption/precipitation. At pH 2 and 8.1, the reduction of TOC was very small. The pH and dissolved oxygen significantly affected the dissolution of iron and the production of OH radicals and changed the roles of phenol removal by the Fenton reaction and adsorption/precipitation. (C) 2011 Elsevier B.V. All rights reserved.