A rifampin-resistant mutant of Cellulomonas biazotea, designated 7 Rf(r), secreted elevated levels of xylanases in vivo. The xylanase and beta-xylosidase production in the mutant was not inhibited in the presence of 5% glucose, cellobiose or glycerol in the solid medium. This mutant showed approximately 2-3-fold enhanced product yield and productivity of cellular beta-xylosidase over the wild type parent in shake flask culture studies when grown on either cellobiose, cellulosic or lignocellulosic (LC) substrates. Extracellular production of xylanase was also significantly (P less than or equal to 0.05) altered in the mutant During growth of C. biazotea mutant derivative on xylan, maximum volumetric productivities (Q(p)) for xylanase and beta-xylosidase were 493, and 30.7 IU/l/h, which were 1.21- and 2.29-fold improved over their respective values from the parental strain. The above values are statistically (P less than or equal to 0.05) higher than the values reported in some other xylanolytic mutant organisms.