In this study, two Fenton (Fe2+/H2O2) and Fenton-like (Fe3+/H2O2) reactions were compared to clarify their roles in phenol degradation under varying H2O2 concentrations, iron dosages and pHs, as well as in the presence of radical scavenger. The results of this study showed that a Fenton-like reaction must proceed concurrently with a classic Fenton reaction, and the concurrent Fenton reaction played a major role in the degradation of pollutants. For the Fenton-like reaction, some oxidation intermediates of phenolic compounds may promote the conversion of Fe(III) to Fe(II) in addition to the uni-molecular decomposition of the Fe(III)-hydroperoxy complexes. The results also showed that varying H2O2 concentrations exerted identical effects on the two reactions, and that phenol degradation in both reactions could be correlated to the decomposition of H2O2. At low levels of iron concentration, the Fenton reaction appeared to be more efficient than the Fenton-like reaction in terms of the phenol degradation and H2O2 decomposition. Additionally, the Fenton reaction had an effective pH range of 2.5-6.0, while the Fenton-like reaction was limited to a narrow pH range of 2.8-3.8. Although the Fenton-like reaction was much slower than that of the Fenton reaction, the overall extent of phenol degradation and H2O2 decomposition at the optimal conditions was equivalent. (C) 2009 Elsevier B.V. All rights reserved.