To utilize hemicellulosic biomass efficiently, the microorganism producing xylanase was isolated from fermented sawdust. It was a Gram positive, aerobic and rod shape bacterium. It had endospore and secreted strong hydrolases, such as amylase and protease. Through morphological, cultural and physiological tests, it was identified as Bacillus sp. GS. To increase the productivity of xylanase from Bacillus sp. GS, the enzyme production medium was optimized. The composition of the medium and incubation conditions were like follows xylan 1.25%, yeast extract 0.1%, NaN030.2%, K2HP04 0.1%, MgSO4 0.02%, mineral salt 0.005%, pH 6.5, incubation temperature 37$^{circ}C$.