Sillenite bismuth ferrite (S-BFO) Bi25FeO40 was synthesized by a hydrothermal process and firstly adopted for the activation of peroxymonosulfate (PMS). Multiple characterization was conducted for the morphology and physicochemical features of S-BFO. Degradation of aquatic levofloxacin (LVF) was thoroughly evaluated by using a coupled process for the decontamination of the typical emerging organics. Some crucial parameters for the activation kinetics as well as economic recyclability were examined with the detailed mechanism proposed. For the first time, singlet oxygen (O-1(2)) was identified as the main reactive oxygen species through radical scavenging experiments, electron paramagnetic resonance spectroscopy (EPR) and HPLC-MS determination. Based on the XPS and EPR results, a catalytic mechanism is proposed concerning the parallel generations of O-1(2): (i) Bi5+ is replaced by Bi3+, resulting in the formation of an oxygen vacancy in the lattice and an active oxygen (O*), which could produce O-1(2) through the reactions with PMS; (ii) direct formation of O-1(2) from radSO-5 generated by the interaction between Bi5+ and PMS. This study demonstrates a novel catalyst for heterogeneous activation of PMS via a non-radical mechanism, which could be alternatively adopted in the decontamination in surface/ground water.