Abstract: The purpose of present study was to determine the effect of dissolved O2 on cellulase and xylanase production by Chetomium thermophile in growth medium of wheat straw. The concentration of dissolved oxygen was optimized through stirring. Kinetic parameters including substrate utilization (g substrate L/h) and enzyme production (IU) was studied from the maximum slope in plots of substrate utilized (g/L) and enzyme produced (IU/L) vs time of fermentation. Specific rate of product formation (QP) and substrate utilization (Qs) was also determined.