A xylose isomerase produced by thermophilic bacterium Anoxybacillus flavithermus was purified using Sephadex G-75 gel filtration,DEAE-cellulose anion exchange chromatography and Q Sepharose Fast Flow anion exchange chromatography.The estimated molecular mass of the purified xylose isomerase was 181 ku and was made up of four sub-groups.The optima temperature and pH of enzymatic reaction were 80°C and pH 7.0,respectively.This xylose isomerase is alkali-tolerant and thermo-stable: the enzyme activity keep about 80% in 70℃ for 1h and keep about 80% in pH5.0～8.0 for 1 h,even keep about 40% in pH12.0 for 1 h.The enzyme was mainly activated by Mn2+ and Co2+ but was mainly restrained by Zn2+,Cu2+ and Al3+.