Thermoalkalophilic Enterobacter sp MTCC 5112 was isolated from a sediment sample collected from the Mandovi estuary, west coat of India. This culture produced extracellular xylanase. The xylanase enzyme was isolated by ammonium sulfate (80 %) fractionation, and purified to homogeneity using size exclusion and ion exchange chromatography. The molecular mass of the xylanase was ~ 43 kDa. The optimal pH of the xylanase activity was 9, and at room temperature it showed 100% stability for 3 h at pH 7, 8 and 9. The optimal temperature for the enzyme activity was 100 ºC at pH 9.0. At 80 oC and pH 9, 90 % of the enzyme activity was retained after 40 min. At 70 oC and 60 oC, the enzyme retained 64 % and 85 % of its activity after 18 h, respectively. While at 50 oC and pH 9 the enzyme remained stable for days. For xylan, the enzyme gave a Km value of 3.3 mg/ml, and Vmax value of 5000 µmol.min-1. mg-1 when the reaction was carried out at 100 oC and pH 9. In the presence of metal ions such as Co+2, Zn+2 , Fe+2, Cu+2 , Mg+2 and Ca+2 the activity of the enzyme increased. Whereas, strong inhibition of the enzyme activity was observed in the presence of Hg+2 and EDTA. To the best of our knowledge this is the first report on the production of xylanase by this bacterium.