Purpose This paper aims to study the ability of laccase for decolourisation of reactive dyes in presence and absence of natural and synthetic mediators. Design/methodology/approach Box–Behnken design was used to optimize the parameters to achieve optimum response value. Preliminary screening using several mediators was performed to evaluate extent of decolourisation for the purpose followed by selection of effective mediators only. Findings Laccase performs in acidic pH; increase in temperature enhances its activity. Rate of decolourisation depends on laccase and dye concentration, temperature, pH and treatment time. Out of five mediators studied, HBT, BT and VA showed promising results. Research limitations/implications Study on decolourisation was conducted for individual dyes. In some cases, dyes are applied in combination which requires further study for authentication of data. Practical implications Decolourisation with laccase has been found to be a promising technology in waste water treatment. However, selection of mediator remains a crucial factor. Social implications Reactive dyes are self-hydrolysed over time under natural conditions and extent of decolourisation depends on concentration of dye discharged and time spent. If not decolourised quickly, it imposes restriction on use of river water for irrigation. Originality/value In this work, activity of various natural and synthetic mediators alongwith laccase was studied to achieve maximum decolourisation which was not studied earlier.