With the view of their importance in photochemical reactions, impacts of five selected parameters (UV wavelength/transmission, perfluorooctanoic acid (PFOA) concentration, dissolved oxygen (DO), solution pH and water quality) on PFOA photodecomposition in water were investigated for the first time in our knowledge. Laboratory batch tests using a glass reactor (1.5 L), a low pressure UV (LPUV) lamp (20 W) and two types of lamp sleeves were carried out. Ultrapure water (UPW), tap water and urban river water were used in "water quality effect" tests, while UPW was used in all other tests. UV wavelength and transmission showed profound impacts on PFOA photodecomposition. The compound was more easily decomposed by vacuum UV (VUV: 185 nm) than by UVC (254 nm). No visible impact of PFOA concentration (0.12-2.42 mu M) on its elimination ratio was observed. The inverse correlation observed between defluorination ratio and PFOA concentration was attributed to UV photon-limited condition for larger PFOA concentrations combined with stepwise photodecomposition of PFOA. DO in reaction solution had negative impact on PFOA elimination, while abundant DO in solution was detrimental for its photomineralization. Though no clear-cut impact of solution pH (3.0-10.0) on PFOA photomineralization was observed, pH 3.0 was relatively better. Water quality also profoundly impacted PFOA photomineralization. Organic constituents and bicarbonates were directly and indirectly responsible for drastic decrease in PFOA photomineralization in organic-rich waters. These findings may serve as basic information for photodecomposition of similar other perfluorinated compounds (PFCs). (C) 2011 Elsevier B.V. All rights reserved.