Polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic pollutants which are abundant and environmentally widespread. Anthracene is a simple PAH that can be oxidized by laccases, copper-containing oxidase enzymes, produced by some plants, fungi, and bacteria. In this work, the extracellular culture fluid (CF) of laccase-producing fungus Pleurotus ostreatus was separated to crude laccase (CL) and aqueous ultrafiltrate (AU) fractions. The rate of anthracene oxidation by CF was 68.7 % while oxidation by CL was only 27.8 %. The addition of AU enhanced anthracene oxidation rate by CL to 60.4 %, indicating that the natural redox-mediators were present in the CF. The laccase-catalyzed anthracene oxidation rate increased with increased AU concentration, implying that oxidation rate is positively related to the concentration of natural mediators when laccase activity is constant. The AU from fungal culture containing bran or straw enhanced laccase-catalyzed anthracene oxidation; this enhancement increased further with prolonged fungus-cultivation, implying that both bran and straw induce the natural mediators. Our findings suggest increasing natural mediator levels may be an alternative strategy to improve the biodegradability of laccase-producing fungi.