The efficacy of different Pleurotus ostreatus (L.) isolates to treat pulp and paper industrial effluent on a shake flask and fermentor were studied. In the shake flask and fermentor studies, Pleurotus ostreatus decolorized the effluent 69.68% and 66.66% respectively, on 7TH day of incubation. The chemical oxygen demand was reduced by 61.3% by Pleurotus ostreatus on day 7 of incubation. Various cultural conditions including different glucose concentrations, nitrogen sources, pH, temperature and incubation period influence on biomass and different enzymes viz; xylanase, CMCase and laccase production by Pleurotus ostreatus IMPP-02 were optimized in shake flask cultures. Under these culture conditions, the maximum level of xylanase activity (9.29 Uml-1), CMCase (7.37 U ml-1), laccase (13.57 U ml-1) and effluent decolorization (69.68%) were observed on 7th day during shake flask studies. Furthermore, the optimum pH and temperature were found to be 5.0 and 30°C, respectively in fermentor studies. The maximum color reduction of 66.66 %; biological oxygen demand (BOD) and chemical oxygen demand (COD) reduction of 65.35 % and 61.3 % respectively, were determined during fermentor studies.