Environmentally persistent and bioaccumulative perfluorooctanic acid (PFOA) was difficult to be decomposed under the irradiation of 254nm UV light. However, in the presence of 80μmol/L Fe(III), 80% of PFOA with initial concentration of 48μmol/L (20mg/L) was effectively degraded and 47.8% of fluorine atoms in PFOA molecule were transformed into inorganic fluoride ion after 4h reaction. Shorter chain perfluorocarboxylic acids bearing C 3 –C 7 and fluoride ion were detected and identified by LC/MS and IC as the degradation products in the aqueous solution. It was proposed that complexes of PFOA with Fe(III) initiated degradation of PFOA irradiated with 254nm UV light.