Twenty six microorganisms were isolated from soil and horse manure samples from in Iowa, U.S. Microorganisms were cultivated and screened by using plate count agar (PCA) at $35^{circ}C$ containing 1% (w/v) oat spelt xylan instead of glucose. The xylanase activities of bacterial strains were analyzed by measuring the concentration of reducing sugar by DNS method. All isolated strains were characterized as the rod form and gram positive strains. Among the isolated strains, the HM6 strains gave the highest xylanase activity. This strain was identified as Bacillus pumilus HM6 by 16S rDNA sequence, morphological and biochemical analysis. Optimal culture temperature and initial medium pH for B. pumilus HM6 were $30-35^{circ}C$ and pH 6-7, respectively. The maximum xylanase activity of 6879 IU/mL was obtained after growth of HM6 with 1% (w/v) oat spelt xylan at $35^{circ}C$ for 6 days. Studies on enzymatic properties showed that the optimum conditions for the highest xylanase activity were $60^{circ}C$ and pH 8.0. In addition, xylanase activity was stable over 2 hours at $50^{circ}C$, whereas activity decreased after 30 min at $70^{circ}C$.