Abstract: The present study is concerned with the effect of carbon and nitrogen sources and their concentrations on the production of xylanase by mutant strain of Aspergillus niger GCBMX-45. High xylanase activities (2350 U/g) were observed when starch (2%) was used as carbon source. (NH4)2SO4 (0.2%) was found to be best nitrogen source for optimum enzyme production i.e., 2480 U/g. The production of enzyme reached maximum, 72 hours after inoculation. All the fermentations were carried out at 30°C at 0.4 cm (10g wheat bran) depth of the basal medium.