•Magnetite nanoparticle was fabricated through a simple routine to activate persulfate.•Hydroxyl radicals dominated the degradation process at acidic condition.•Both free and surface bound radicals existed in the oxidation system.•Transformation of piperazinyl ring was the primary degradation pathway. Uniform magnetite nanoparticles (MNP) were prepared through a facile hydrothermal routine and subjected to the heterogeneous activation of persulfate (PS) to degrade norfloxacin (NOR). The degradation efficiency reached 90% within 60min (the concentration of NOR and PS was 15μM and 1mM, respectively; dose of MNP: 0.3gL−1; pH: 4.0). However, it was greatly inhibited with the increase of pH, especially at basic condition (pH0=9.0). This was probably due to the precipitation of the ferrous ions leached from the surface of MNP. In addition, hydroxyl radical was found to dominate the degradation process at acidic condition while both sulfate and hydroxyl radicals contributed to the degradation at neutral condition. Except the leached form, the structural ferrous ion on the surface of MNP also participated in the activation process through the redox reactions, as illustrated by the X-ray photoelectron spectroscopy (XPS) analysis. Finally, four degradation pathways were tentatively proposed based on the identified intermediates and the transformation of piperazinyl ring seemed to be the primary one.