Long term ecological and physiological toxicity caused by the residuals of fluoroquinolones (FQs) in the aquatic environment has raised much attention. Ciprofloxacin as a typical FQs was degraded by UV activated persulfate,which was a new advanced oxidation technology. The degradation products were characterized using qualitative and quantitative methods,and the detailed degradation mechanism and pathways of ciprofloxacin by UV/persulfate were proposed by using the analysis results of quantum chemistry and mass spectra. The results revealed that the optima condition for CIP degradation was pH 9.0. After a 30 min reaction,13 intermediates were identified in the solutions,including alcohols,phenols,ketones and amides. The concentrations of several intermediates exhibited an up and down trend. Oxidations mainly occurred at the C F bond and carboxylic acid on quinolone group,as well as piperazine group. The degradation of CIP by UV/PS mainly included four pathways,and a series of defluorination,photolysis,substitution,addition and deamination were observed,leading to the final open ring reaction of target compound.