The main aim of this research work was to decolorize various azo dyes and reactivedyes from lab-scale dye solutions and real textile wastewater samples under high salt concentration conditions.Decolorization experiments were run using a recentlyisolated halophilic bacterium Gracilibacillus sp.GTY.As a new bacterial strain，someother investigations，such as isolation，characterization and study of a largeextrachromosomal DNA were also taken place. So the dissertation is presented indifferent steps bellow. Firstly，a highly salt tolerant strain obtained from Dalian coastline，was identified asGracilibacillus sp.GTY on the basis of morphological and physio-biochemicalcharacteristics and 16S rDNA sequence analysis.According to DNA sequence，themaximum 93％-95％ homology was found for the strain GTY.The strain wasdeposited as a patent strain in China General Microorganism Culture Center with theaccession number CGMCC 1527.The 16S rDNA sequence of GTY was alsosubmiaed to GenBank with the number DQ 286727.The strain was gram-negative，rod-shaped and strictly aerobic.0ptimum growth conditions were observed：temperature+300℃，pH 7.2, 10％-15％(w/v) of NaCl，and proline as the bestcompatible solute as well as a good carbon source.The rapid and smooth growth rateswere observed in 10％-15％(w/v)of NaCl supplemented Luria-Bertani(LB) and Mineral-Salt(MS)media，but the strain could survive narrowly in the mediacontaining up to 25％(w/v)of NaCl.So it was considered as a highly salt tolerantstrain. Secondly，a large molecule of extrachromosomal DNA was isolated from the strain bya modified method.Then this plasmid DNA was eliminated by acridine orange toknow its role in host genome.After successful elimination，it was assumed that the plasmid contains some key genes，which may be responsible for the bacterial salt tolerance. Thirdly，an attempt was made to optimize conditions for the bacterial decolorizationof various dyes in lab-scale dye solutions under high salinity conditions.Decolorization experiments were conducted by growing and resting cells as well asazo reductase.Experiments were performed under different concentrations of NaCl.Detailed analytical investigations were performed using only one of the azo dyes，Acid Red B.For growing cells，strain grown in media containing 10％-15％(w/v)ofNaCl showed the best performance of azo dye Acid Red B decolorization. Dye was almost completely decolorized(nearly 100％)after 96h of treatment.Strain grown inthe media containing 2％-5％(w/v)of NaCl showed very poor decolorization abilitywhere bacterial growth rates were very poor also.0n the other hand，strain grown inthe media with the highest percentage(25％，w/v)of NaCl showed moderatedecoiorization ability.Strain grown in lower percentages of NaCl could not showgood performance of decolorization because of low growth rates.Decolorization was not satisfactory also in the media containing 25％(w/v)of NaCl，because theinhibition to microorganisms by high salt concentration，which may cause plasmolysisand/or loss of activity of cells.Resting ceils also showed the best performance of decolorization in 10％-15％(w/v)of NaCl.Extracted azo reductase was non.purified Dalian University of Technology Doctoral Dissertationand non-characterized.The decolorization of dye was conducted in 3 ml of reactionmixture at 30℃ in 700 sec. Reaction rate obtained from time course spectrameasurement analysis was comparatively slow. The percentage of dye removal was about 10％in the reaction mixture. Finally，several experiments were set up to degrade a textile azo dye Acid Red B andremove COD from a real textile wastewater body.The textile wastewater sample wasnaturally salty(10％ of Na2S04)，and COD value was relatively high.The textilewastewater sample was used by adding certain nutrients and NaCl for the propergrowth of this salt tolerant strain.The study was conducted on the basis of variousenvironmental fIactorS and substrates.Dye degradation and COD removal rates werecomparatively slow in first two days. Decolorization efficiency might be attributed to the microbial shock due to the change of environment and the possible toxic orinhibitory effects of certain compounds of the textile wastewater on the microbe. Nevertheless，after an acclimatization period of 6-10 days，the anaerobic microbesretained their activity leading to wastewaters decolorization efficiency of nearly 96％ in optimum growth condition.Then COD removal rate was also satisfied.Afterdecolorization，COD removal was observed 4436.87(mg/l)where the initial COD value was more than 7000(mg/l).