The degradation of metoprolol in aqueous solutions by traditional Fenton-like reaction (Fe-III/H2O2), and Fe-III-NTA modified Fenton-like reaction (Fe(III)NTA/H2O2) in the absence and presence of Mn-II (Fe-III-NTA/ H2O2-Mn) have been investigated. The results show that Fe-III-NTA/H2O2 is able to degrade metoprolol at initial neutral pH. In particular, the presence of Mn-II greatly improved the degradation rate of metoprolol by Fe-III-NTA/H2O2 over a wide pH range of 4.0-8.0. Under the same conditions, the degradation rate constants of metoprolol (k) obtained in Fe-II-NTA/H2O2-Mn system were typically 7-9-fold larger than those obtained in Fe-III-NTA/H2O2 system. The involved reactions in Fe-III-NTA/H2O2-Mn system were proposed on the basis of important parameters analysis including ferrous ion concentration, dissolved oxygen (DO) concentration, and the quenching experiments for hydroxyl radial (HO') and superoxide anion radical (O-2(.-)). Several intermediates have been identified by mass spectrometry. Our results suggest that the degradation of metoprolol in both Fe-III-NTA/H2O2 and Fe-III-NTA/H2O2-Mn systems were caused by HO. attack. The degradation pathways of metoprolol were proposed on the basis of the identified intermediates. Fe-III-NTA/H2O2-Mn system led to more efficient degradation of metoprolol and its intermediates. (C) 2016 Elsevier B.V. All rights reserved.