The Fe3O4/SiO2/polythiophene (FSP) submicron composite (SC) with a structure of semiconductor/insulator/semiconductor (SIS) was obtained. The characterization results showed that the FSP SC had a spherical core/shell shape with an average diameter of 506 nm. The high saturated magnetization value (similar to 39 emu/g) ensured the easy separation of FSP SC from aqueous solution. The photo-catalytic activity of the FSP SC was evaluated by the degradation of methyl orange (MO) under UV-irradiation in the presence of H2O2. Due to the SIS structure, the degradation rate constant by FSP SC (0.02177 min(-1)) was 6.4, 1.6, and 2.5 times higher than that of Fe3O4/polythiophene (FP), polythiophene (P), and TiO2, respectively. The repetition results suggested the good photochemical stability of FSP SC. The mechanism was proposed by investigating the energy band variation of the SIS structure, the transfer of light generated carriers and the formation of effective hydroxyl radicals in the photo-catalysis progress. (C) 2014 Elsevier B.V. All rights reserved.