Abstract: The paper presents the effects of Mn~2+ on white rot fungus, Phanerochaete chrysosporium, particularly in its production of the extracellular enzymes, lignin peroxidases (LiP) and manganese peroxidases (MnP) in the biodegradation of chlorophenols. The presence of Mn~2+ resultes in more production of MnP and less production of LiP. Degradation of low molecular weight chlorophenols by white rot fungus takes place mainly inside the cells by intracellular enzymes, and the overall degradation rates are increased by the fungus enzymes. The presence of Mn~2+ enhances the observed degradation rates, suggesting that MnP plays a more important role than LiP in the degradation of chlorophenols. Relative to activated sludge-mixed liquors, the white rot fungus has a much lower affinity to chlorophenols, making it ideal for pretreatment of wastewaters containing high concentrations of such compounds. The toxicity tolerance of white rot fungus, which is similar to that of the activated sludge, may be improved when a more appropriate treatment process and/or more optimum treatment conditions are employed.