This paper concentrates on the application of the fungus Pleurotus ostreatus, in decolourizing the azo dye Dimaren blue HFRL. The efficiency of purified laccase in biodegrading various textile dyes has been demonstrated using commercially used textile dye Dimaren blue HFRL in solid plate assay, liquid form and enzymatic degradation. In solid plate assay decolourization study it has been found that P. ostreatus is able to decolourize 93.67% Dimaren blue HFRL in 10 days. In liquid media (basal medium) decolourization study has shown that P. ostreatus is able to decolourize 85% Dimaren blue HFRL in 10 days. In enzymatic degradation parameters, such as temperature and pH concentrations have been-optimized. The laccase enzyme has exhibited the highest decolourizing activity at an optimum temperature of 40°C and at an optimum pH of 5.0. Therefore, it has been proved that P. ostreatus is a potential candidate species in colour removal from textile dyeing industry effluent. © 2019 Scientific Publishers. All rights reserved.