Textile industry wastewaters are characterized by high wastewater volume, alkaline pH, and colors that depend on dyes used in process. The composition of wastewater in textile industry is variable due to raw materials, dyes of different color, chemicals, different processes, various technologies; water use and wastewater quality. The major pollutant parameters in textile industry are BOD, COD, SS, oil and grease, total Cr, phenol, sulfide, temperature, pH, sulfide compounds, TOC and turbidity. Additionally, depending on dyes and chemicals used, many kinds of heavy metals and organic pollutants exist in textile wastewaters based on the subcategory of production such as cotton, wool and synthetic goods that lead to different wastewater characterization. The selected textile industry deals with synthetic textiles and similar products generating dyeing wastewaters. There are 3 parallel sequencing batch bioreactors (SBR) in the wastewater treatment system. The activated sludge biological wastewater treatment system indicates different microbiological structure because of its inconstant influent characteristics. For this reason, the treatment system has frequently been facing performance problems. In this study, the textile industry wastewater characterization was performed and floc structure of the activated sludge and microorganisms were investigated. The general and dominant microbial populations were identified both qualitatively and quantitatively.