Abstract: Xylan was extracted from oat spelts and confirmed using UV spectrophotometry. Nine hundred and fifty-five isolates of fungi from air, water, mud and soil samples from hypersaline, alkaline lakes of Wadi-El-Natrun were screened for their ability to produce xylanase along with carboxymethyl cellulase (CMCase) using sucrose-free Czapek’s agar medium supplemented with 1 % xylan as carbon source. Three hundred and twenty-two isolates out of 955 were xylanase producers (142 high, 108 moderate and 72 low producers). From the high producers, the most active 8 strains were selected and screened for their capabilities of production of extracellular xylanase and CMCase in submerged fermentation using sucrose-free-Cz broth amended with 1 % xylan. pH, nitrogen source and temperature were optimized for the maximum production of xylanase and CMCase by these strains. The most active eight strains showed species and strain variations in their optimal culture conditions. Four strains showed their maximum xylanase production at pH 11 including A. fumigatus AUMC 10333, A. fumigatus AUMC 10334 at pH 7, A. flavus at pH 9, Corynascus sepedonium at pH 5, and A. fumigatus AUMC 10332 at pH 3. On the other hand, the three strains of A. fumigatus and A. oryzae exhibited their maximum production of CMCase at pH 11, two strains at pH 7, one strain at pH 9 and one strain at pH 3. With regard to the nitrogen source, the eight strains showed also various capabilities for the maximum production of the two enzymes. Some strains preferred yeast extract or peptone while others preferred NaNO3, NaNO2 or NH4Cl. The most active two strains, Aspergillus oryzae and A. flavus were screened for xylanase and cellulase production at different incubation periods, NaCl concentrations and xylan from different origins. The addition of NaCl promoted the production of the two enzymes to a maximum in case of xylanase production at 3.5 % NaCl by A. flavus, and at 2 % by A. oryzae, and at 4.5 % and 5 % in case of CMCase production by A. flavus and A. oryzae respectively. Xylan from birchwood was the best source for the yield of xylanase and from wheat bran was the best for cellulose whereas xylan from alkali-treated corn cobs was superior for both enzymes Key words: Xylanase, cellulase, extreme habitats, Wadi-El-Natrun lakes.