Dyes are released into the environment from industrial wasterwater. They are considered to be a pollution problem because of the wide spread into environment with a variety of colors. In order to biological treatment of industrial dyes waste water, biodegradation of reactive dyes such as Rifacion Red H-3EB, Rifazol Blue BT, Rifacion Yellow P-4G and Rifacion Brown RT were carried out decolorized by Aspergillus sojae B-10. Aspergillus sojae B-10 showed the almost completely biodegradation ability when it was cultivated in a 2.0% glucose, 0.06% sodium nitrite, 0.1% $KH_2PO_4$, 0.5% $MgSO_4cdot 7H_2O$ containing each reactive dyes (500 ppm) under the optimal conditions of 32$circ$C and pH 5. The mycelium of Aspergillus sojae B-10 was produced extracellular enzyme which has concerned responsible for dyes biodegradation. Under optimal conditions, reactive dyes started being decolorized within 24 hr and its was almost decolorized c ompletely after 5 days incubation. Rifazol blue RT was not completely decolorized until 5 days of cultivation. Rafacion Red BT, Rifasol blue BT and Rifacion yellow P-4G were completely decolorized after 5 days cultivation.