In this study, fungal isolate D2-1 was isolated from contaminated soil collected from textile industry companies and showed high potentiality for decolorization of two different azo dyes. This isolate was identified as Aspergillus niger D2-1 using morphological and cultural characteristic as well ITS gene sequencing. Decolorization process under different optimized condition of azo dye concentration, pH, incubation periods, temperature, inoculum size and different carbon and nitrogen sources were investigated. The maximum decolorization efficiency against 100 ppm dye concentration of reactive yellow (4GL) and reactive red (4BL) dyes of 98.62 % and 92.42 %, respectively, were recorded for Aspergillus niger D2-1 at pH 9.0, in presence of 2 % glucose and 0.5% yeast extract as carbon and nitrogen sources respectively at room temperature after 7 days on shaking conditions. The decolorization percentage was confirmed by ultraviolet-visible (UV-Vis) spectrum analysis of untreated/treated reactive yellow (4GL) and reactive red (4BL) dyes, which showed complete disappearance of peaks at ~ 425 nm and at ~ 520 nm, indicates the degradation of dyes due to fungal activity. Treatment of textile wastewater effluent by Aspergillus niger D2-1 showed high decolorization percentage (59%) for effluent, also physico-chemical characteristics of textile effluent such as chemical oxygen demand (COD), total dissolved solids (TDS) and total suspended solids (TSS) were decreased from 756 mg/L, 1597 mg/L and 821 mg/L to 391 mg/L, 845 mg/L and 362 mg/L respectively. Moreover, Gas chromatography - mass spectroscopy (GC-MS) of textile effluent before and after treatment were recorded and confirmed the potentiality of Aspergillus niger D2-1 in dyes wastewater treatment.