Abstract: Effect of ammonia pretreatment of cellulosic wastes on xylanase production was studied using two microfungi, Aspergillus niger ANL301 and Penicillium chrysogenum PCL 501. Xylanase activity of culture supernatants of the two microfungi, fermented in basal media containing as sole carbon source pretreated and non-pretreated wastes (sawdust of Mitragyna ciliata, sugarcane pulp and wheat bran), was measured at 24 h intervals for 120 h. Ammonia pretreatment of the cellulosic wastes enhanced xylanase production by the organisms, inferred from the activity of extracellular xylanase enzyme (endo-β-xylanase: EC 3.2.1.8). Pretreatment of sawdust increased the optimal specific xylanase activities of A. niger ANL301 and P. chrysogenum PCL501 by 40.2 and 192.7%, respectively. An increase of 72.9 and 63.5% in optimum activity was obtained for A. niger ANL301and P. chrysogenum PCL501 respectively by ammonia pretreatment of sugarcane pulp. Pretreatment of wheat bran gave a marginal increase of 3.3% in the optimum xylanase activity of A. niger ANL301 and 143.4% activity increase for P. chrysogenum PCL501. The present results show that ammonia steeping of the agro-wastes significantly improved xylanase production by the microfungi. The pretreatment method is a cost-effective means for producing xylanases from cellulosic wastes.