Resupinate white rot fungi were isolated from across Thailand (seven provinces) and evaluated for their ability to degrade the recalcitrant and toxic dye reactive black 5 (RB5). Seven of the 13 isolates decolorized RB5 (100 mg/L) within three days (greater than 50%). One isolate, Phanerochaete sordida PBU 0057, yielded complete decoloration within three days. It was active under environmental conditions in which waste dyes are discharged. The degradation of RB5 by P. sordida PBU 0057 was confi rmed by spectrophotometric and HPLC analyses. The degradation was associated with the activities of laccase and lignin peroxidase. Manganese peroxidase was additionally active in the comparative control strain of P. chrysosporium. The degradation dye products produced by P. sordida PBU 0057 were not phytotoxic towards Phaseolus vulgaris, Sorghum bipolar, and Zea mays. Overall, P. sordida PBU 0057 showed somewhat greater dye-degradative activities when compared to the control reference strain P. chrysosporium ATCC 24725 under practical environmental conditions. P. sordida PBU 0057 has potential for application in the biological detoxifi cation treatment of waste dye residues.