Jonesia denitrificans BN-13 produces six xylanases: Xyl1, Xyl2, Xyl3, Xyl4, Xyl5, and Xyl6; the Xyl4 was purified and characterized after two consecutive purification steps using ultrafiltration and anion exchange chromatography. The xylanase-specific activity was found to be 77 unit (U)/mg. The molecular weight of the Xyl4 estimated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a monomeric isoenzyme of about 42 kDa. It showed an optimum pH value of 7.0 and a temperature of 50 A degrees C. It was stable at 50 A degrees C for 9.34 h. The enzyme showed to be activated by Mn+2, beta-mercaptoethanol, and dithiothreitol (DTT) with a high affinity towards birchwood xylan (with a K (m) of 1 mg ml(-1)) and hydrolysis of oat-spelt xylan with a K (m) of 1.85 mg ml(-1). The ability of binding to cellulose and/or xylan was also investigated.