Abstract: The presence of textile dyes in wastewater of textile factories represent a major environment problem threatening the aquatic life. The decolorization of such harmful products is the major field of interest in research. In this study, Aspergillus niger, a brown rot fungi, isolated from the soil samples around the textile distillery industries of Al-Mahala Al-kobra, Egypt was evaluated for its efficiency in decolorization of different textile dyes; reactive red 198 (RR 198), reactive orange 122 (RO 122), reactive yellow 160 (RY 160), reactive blue 21 (RB 21) and reactive blue 19 (RB 19). Aspergillus niger showed a strong ability to decolorize various reactive dyes (azo, phthalocyanine and anthraquinone dyes) after 4 days. The decolorization was effective in an acidic environment (pH 4). Aspergillus niger grew well in a high concentration of dyes (500 mg L–1), resulting approximately in 100% decolorization extent in 5 days with RB 21, RB 19, RR 198 and RO 122 and could tolerate up to 1000 mg L–1 of dyes. The decolorization was more effective in the presence of sucrose. The Reactive Yellow 160, a diazo dye, was more resistant to decolorization by Aspergillus niger than the other dyes. High decolorization extent and facile conditions showed the potential for the Aspergillus niger to be used in biological treatment of textile dyes.