Xylanase producing alkaliphilic bacteria are bacteria that can grow well in alkaline environment. They can produce xylanase that optimum at high pH to hydrolyze xylans to be xylooligosaccharides and xylose. The calcareous soil with pH more than 7,3 can be xylanase producing alkaliphilic bacteria nature habitat. The aims of this research were (1) to isolate xylanase producing alkaliphilic bacteria isolated from calcareous soil in limestone hill area Krakitan, Bayat, Klaten and (2) to determine the kind of xylanase producing alkaliphilic bacteria which has high xylanolytic activity. For isolation and selection of xylanase producing alkaliphilic bacteria, the alkaline medium pH 9-10 were used, and 0,5 % oat spelt xylan was added. The calcareous soil was taken from limestone hill area and then was filtered and inoculated on to alkaline medium. After that, they were incubated in shaker incubator for 3 days at 150 rpm in 30-37Â°C. Then, the enrichment sample was grown in the same medium, that 1,8% agar was added. The colonies that grew and produced clearing zone which had the highest xylanolytic activity were chosen then characterized and identified. The growth ability isolates were examined in xylan medium at pH 7, 8, 9, 10, and 11 in order to decide bacteria of fakultative or obligate alkaliphilic. Xylanase producing alkaliphilic bacteria could be isolated from calcareous soil in limestone hill area Krakitan, Bayat, Klaten. The identified 10 xylanase producing alkaliphilic bacteria that had xylanolytic activity were Pseudomonas HT-1a, Pseudomonas HT-1b, Bacillus HT-2a, Bacillus HT-2d, Flavobacterium rigense HT-3c, Micrococcus luteus HT-3d, Paracoccus alcaliphilus HT-5c, Alcaligenes HT-4c, Alcaligenes HT-5a, and Alcaligenes HT-5b.