In this paper, the heterogeneous Fenton and UV/Fenton catalytic activities of transition metal substituted magnetites, Fe3-xMxO4 (M=Ti, Cr, Mn, Co and Ni), were compared in the perspective of (OH)-O-center dot radicals generation. In heterogeneous Fenton reaction, the substitutions of Cr(III), Mn(II) and Co(II) enhanced the rate of (OH)-O-center dot formation, while Ni(II) and Ti(VI) showed the negative effect. In heterogeneous UV/Fenton reaction, the Ni(II) and Co(II) introduction did not show notable changes on (OH)-O-center dot generation efficiency, whetreas the Cr(III), Ti(VI) and Mn(II) incorporation improved this reaction and accordingly enhanced the UV/Fenton catalytic activity of magnetite. Redundancy and Pearson correlation analyses were carried out to interpret the influence factors in Fenton and UV/Fenton reactions. (C) 2014 Elsevier B.V. All rights reserved.