1444 microorganisms were isolated from soil samples from the northern Thai and screened at 55 degreesC by using basal medium supplemented with 1% carboxymethyl cellulose as a sole carbon source. One isolate, Streptomyces Ab106, had a high activity of a cellulase-free xylanase also without mannanase activity. The maximum cellulase-free xylanase activities of 3.5, 3.3, 3.1 and 2.7 IU were after growth of the organism with 1% (w/v) corn hull, corncob, bagasse and oat spelt xylan, respectively, at 55 degreesC for 6 days, respectively. The activity was more than 5 times higher than that at 35 degreesC.