Effects of natural organic matter (NOM) on the degradation of chloramphenicol (CAP) by UV/H2O2 and the characteristics of degradation products were investigated. With initial concentration of 5 mg L-1 CAP, UV and 0.5 mM H2O2 process induced the degradation rate constant increased to 3.75 x 10(-3) s(-1), which was about 1.6 times of that treated with UV alone. The excitation-emission matrix (EEM) fluorescence spectra showed that the degradation products included many humic acid-like compounds (HA). Therefore, addition of 5 mg/L HA to the solution decreased the degradation rate constant to 1.78 x 10(-3) s(-1), because they would compete for the oxidizing reaction of CAP with OH. However, the degradation rate constant and removal efficiency of CAP were influenced not only by the initial concentration of HA but also by the ratio of [HA](0)/[CAP](0). When the initial concentration of CAP decreased to 0.1 mg/L, the ratio of [HA](0)/[CAP](0) increased to 50. The degradation rate constant increased to 2.32 x 10(-3) s(-1). Moreover, the results of ultra high-performance liquid chromatography & quadrupole time-of-flight mass spectrometer (UPLC-Q-TOF-MS) suggested that the main degradation products were dichloroacetic acid (m/z 129) and aromatics 4-nitro-benzoic acid (m/z 167). These products were induced by the radical reaction during the UV/H2O2 treatment process. Meanwhile, Fourier transform infrared spectroscopy (FTIR) indicated that UV/H2O2 could destroy the aromatic ring of CAP and initiating the mineralization of CAP. TEQ(4-NQO) decreased to 0.20 mu g L-1 after the treatment with UV dose 2000 mJ cm(-2) and 0.5 mM H2O2. Therefore, the radical reaction and mineralization of CAP also decreased the genotoxicity obviously.