Textile Industry is amongst the top ranked industries that generate a huge volume of wastewater. Colored effluents are associated with the production and use of dyes, the presence of dyes in aquatic systems has become a serious environmental problem. It is hard to treat those wastes with conventional treatment technology and the major issues with such effluents are color with high pH and total dissolved solid (TDS), chemical oxygen demand (COD) and TSS.The main objective of this study was evaluating dye degrading efficiency of alkaliphilicbacteria isolated from Rift Valley Alkaline Lake and Textile Industry effluent. Mud samples were collected from Lake Abaya, Chamo and Bahir Dar textile industry. Dye degrading bacteria isolation and Enrichment were done using mineral salt medium (MSM) containing 100mg/L of the model dye (Reactive Red141)under anoxic condition. From the enriched sample, a total of 10 Morphological different bacterial colonies were isolated. After individual isolates, six isolates named (CDB2, CB3, TB5, AB7, AB8, and ABD2) were selected. The selected six best isolate mixed cultures were systematically screened and evaluated by their dye degradation efficiency under different nutrient sources (carbon and nitrogen), environmental conditions (temperature, pH, dye concentration) and inoculums size. The results showed that higher decolorization efficiency, 100%, was found at pH 11at a time of 96hr. A decolorization efficiency of 99.88, 94.51%, 84.19% and 71.89% respectively was achieved for sucrose, glucose, acetate and carbon free nutrient supply for the six mixed culture. Whereas the Decolorization capacity of nitrogen source of yeast extract, peptone, NaNo 3 and nitrogen free have 96.98%, 96.93%, 96.82%, and 74.89% respectively. Statistical analysis results also showed that carbon and nitrogen sources havesignificant (p<0.05) effect on the decolorization of (RR141) dye by the selected mixed culture isolates. The decolorization potential of the selected best isolate wasalso significantly affected by inoculums (p<0.05). The best isolates were also shown best decolorizing capacities under a range of temperature (25 - 45˚C). Over those temperature ranges a dye decolorize of 98.31% - 100 % was found within 96hr incubation period under alkaline pH range (11, 10 and 9).Anoxic culture conditions have been found to be favorable for dye degradationbecause it is a well-knownfact that decolorization performance of most alkaliphilic bacteria is better in presence of low oxygen content. The decolonization performance of each pure isolates and there mixed culture under at different carbon and nitrogen source has been studied among this Sucrose has good co-substrate for the decolorization of dye. With respect to nitrogen source, Yeast extract were good organic nutrient for the biodegradation of RR141.Dye concentration also plays a significant role for the Decolorization of RR141 dye. Inoculums’ size has significant (p<0.05) effect on decolorization. Generally, the bacterial isolated from alkaline Lake (LakeAbaya, Chamo and Bahirdar textile waste water) in this study have been significant potential to treat textile wastewater, bacteria isolated from Abaya was more efficient bacteria. further success full advantage should be done on mixed dye effect,Identification of iv the isolate at molecular level and salt effect on microbial decolonization of textile azo dye and HPLC analyses, recommended for the analysis of azo dye degradation The best six isolates of this research are recommended and mixed culture was more recommended than pure culture for treatment of textile wastewater to be tested in real textile Industry treatment plants using appropriate bioreactors. Keywords:Alkaliphilic bacteria; Biodegradation; Decolorization; Alkaline Lake; Reactive Red 141