A pyrite-catalyzed reaction was used to degrade chloramphenicol. Chloramphenicol could be almost 100% removed within 60 minutes when 1 mM H2O2 and 0.1 g/L pyrite were added at an initial pH = 3. During oxidation, intermediates such as nitrobenzaldehyde and dichloroacetamide were identified by gas chromatography/mass spectrometry (GC/MS). The •OH was identified by electron spin-resonance spectroscopy. Pyrite was digested to determine elements by ICP (inductive coupled plasma emission spectrometer). To understand the reaction mechanism and the role of natural pyrite in these processes, techniques including scanning electron microscopy and energy dispersive spectrometry were employed to characterize the solid sample. The results explain that pyrite acts as a ‘bond’ between Fe3+ and H2O2, and this pathway continues to form •OH and inhibit the quenching reaction. Therefore, pyrite-catalyzed reactions would proceed even in low concentrations of H2O2.