The removal of phenol by peroxidase-catalyzed polymerization was examined using the Coprinus cinereus peroxidases at different levels of impurity with respect to contamination. The phenol removal efficiency was improved by lowering the peroxidase purity. Acidic and high molecular weight proteins present as impurities in the peroxidase solution had some positive effect on the phenol-polymerizing reaction. The residual enzyme activity, either only in the solution or both in the solution and on the precipitate during the polymerizing reaction, was measured. The results indicate that the main effect of impurities in the peroxidase solution was the suppression of the adsorption of peroxidase molecules on the polymerized precipitate.