Peniophora cinerea is a white-rot fungus with ability to decolorize dyes in saline textile effluent. After cultivation in a medium composed by sucrose, corn steep liquor, copper, and other minor components, P. cinerea produced 1000 U/L of laccase, but no lignin peroxidase or manganese peroxidase. The produced laccase was purified by precipitation with ammonium sulfate (80%) and anion exchange chromatography. Isoelectric focusing revealed a total of eight salt tolerant laccase isoenzymes with pI between 3 and 6, and molecular weights in the range of 26.2 and 72.6 kDa. Five compounds were then tested and compared for their ability to act as mediators in the decolorization of the reactive blue 19 dye by these laccases of P. cinerea. Syringaldehyde was the best mediator since it increased in almost 3-fold the dye decolorization when compared to the decolorization by using laccase alone. Addition of Mn2+ and oxalate to this system increased in 4.8-fold the initial decolorization rate (178 μmol/L min). When applied for real effluent decolorization, this system promoted the highest decolorization after 72 h at 50 °C and pH 4. This laccase-mediator system was considered promissory for application on the treatment of industrial dye effluents.