Textile industries annually consume a large volume of water through wet processes and consequently produce contaminated wastewater. Textile wastewater contains different chemical materials. Textile dyes are one of the important parts in effluent that have many disadvantages on human body and aquatic organisms. Many different methods have been reported for decolorization of textile dyes in wastewater including: physical methods (filtration, irradiation), chemical process (ozonation, oxidation) and biological treatments. Among the all dye kashida; TEXT-ALIGN: justify; LINE-HEIGHT: normal; TEXT-KASHIDA: 0%; TEXT-INDENT: 0in; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr" In this work a fungi, Aspergillus niger, and a yeast, Candida tropicalis , was used for decolorization of disperse azo dyes. Decoloration mechanism of two different mono azo disperse dyes (C.I. Disperse Blue‌ 183 and C.I. Disperse Red‌ 1), one disazo disperse dye (C.I. Disperse Yellow 23), and an antraquinon disperse dye (C.I. Disperse Blue 56) was investigated. Nutrient agar, sabouraud dextrose agar and potato dextrose agar cultures applied for growing microorganisms, then decolorization process was done in nutrient Broth and sabouraud dextrose broth mediums. Decolorization with Aspergillus niger was carried out in two methods; in first method niger was grown in culture medium contain dye solution, and in second method dye solution was added to the culture medium of pre grown fungi. In first method complete color fading took placed in 4 days, while in second method, time decreased to 30 hours. .Decolorization rate and efficiency were investigated under different initial pHs of 4.5, 6, 7.5, 9 and also different initial dye concentration at 330, 230 and 180 mgL -1 . Results showed there is no significant growing in basic cultures but in acidic cultures, enough growth happened and as a result dyes rapidly absorbed into the fungi body ma decolorization time was about 5 to 7 hours. Decolorization with yeast carried out in aerobic and anoxic conditions in three initial concentrations for antraquinon and red azo dyes, Decolorization efficiency was about 93% for azo red dye and 54% for antraquinon blue dye in aerobic condition and 77% and 73% in anoxic condition respectively. Decolonization results were measured using UV-Vis spectrophotometer in visible region. Dye biosorption into fungi biomass was measured after extraction by acetone and resulted the lowest adsorption for azo red dye (about 50% compare to 78% for blue dye). Liquid chromatography (HPLC) and FTIR spectroscopy analysis were done to identify the biological degradation and possible fragmentation formed during treatment. Results proved chemical degradation in all three azo dyes in addition to biosorption Decolorization. Keywords : Wastewater, biologic decolorization, Aspergillus niger, Candida tropicalis, HPLC, FTIR