In the present study, peroxidase from fenugreek (Trigonella foenum-graecum) seeds was used for the oxidative degradation and polymerization of an organophosphorus pesticide, methyl parathion. Methyl parathion was recalcitrant to the action of fenugreek seed peroxidase. In order to oxidize methyl parathion effectively byperoxidase, the role of some redox mediators has been investigated. The maximum oxidation of methyl parathion was observed in the presence of 0.3 mM phenol, 0.8 mM H2O2, and 0.5 U mL−1 of fenugreek seed peroxidase in the buffer of pH 4.0 at 40°C for 2.5 h. The oxidation of methyl parathion by peroxidase was quite effective in batch process, 71% the compound was removed in 7.5 h. The absorption spectra of treated methyl parathion exhibited a marked difference in the absorbance at different wavelengths as compared to untreated compound. © 2010 American Institute of Chemical Engineers Environ Prog, 2011.