This experiment work was carried out in the lab of Jahangirnagar University, Savar, Dhaka, in 2004. In order to isolate desired thermophilic fungi from different habitats, samples from matured hot piling bins, caddis, jute dust, damaged and rotten jute and jute goods, retting water, rotten wood, root, leaf, straw, cow dung, saw dust were collected from different places of Bangladesh. Samples were usually kept in sterilized containers. Before inoculation of the samples certain amount was taken in a conical flask containing 50 ml of distilled water and warmed at 70°C for 30 minutes to isolate the thermophilic fungi. Microorganisms were isolated on dilution plate method at 60°C. Isolated colonies were randomly picked up and purified. Enzyme activity was determined by the hydrolysis of substrate incorporated, generally as main carbon source in solid agar medium. The activity was detected around the colonies by the appearance of clear zones revealed by the substrate clearness or decolouration. For detecting the xylanolytic activity, isolated fungus was grown on Larch wood xylan containing agar medium. After 3 days incubation, the plates were flooded with 96% ethanol and kept for 4 hours. The fungi, which reveled a large clear zone of hydrolysis around the colony, were selected as lignocellulose degrader. Two strains (M3 and M17) showed the highest xylanase activity were used for enzyme production. M3 and M17 were identified (from CABI Bioscience, UK) as Thermomyces lanuginosus. To study the effect of different lignocellulosic materials i.e. wheat bran, rice bran, sugarcane bagasse, jute dust and saw dust on enzyme production by the selected strains, 50 gm of each raw material were used as carbon source for the growth of the strains. 50 gm of each raw material was taken in lL conical flask and moistened with 35/ml distilled water. The flask was steam sterilized at 15 psi, 121°C for 20 minutes. No additional nutrients were added. Each flask was inoculated with equal number of spores and was grown for 5 days at 55°C. The relative humidity was maintained between 60-70% inside the incubator. After 5 days of incubation, 250 ml of 1 % NaCl solution was added in the fermented mass and again kept at 50°C for 2 hours with occasional shaking. The fermented slurry was first filtered with nylon cloth and than with Millipore membrane (Porosity 0.21l). To study the effect of media composition on xylanase production four days old culture of fungal isolates were suspended in 5 ml of sterilized water from where 1 ml was transferred into each flask containing 100 rnl of different liquid media i.e. PDA, MEA, wheat bran, saw dust and Czapeck's medium. The inoculated culture medium was incubated in an orbital shaker with the speed of 150 rpm at 55°C for 5 days. The fermented slurry was then centrifuged at 8000 rpm for 20 minutes to remove mycelia. The optimum temperature for xylanase production by the strains was studied as follows: equal volume of spore suspension (lml) was added in each flask containing 50 mg of wheat bran with pH 6.0 and 70% moisture. The flasks were incubated at different temperatures such as 35, 40, 45, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 and 60°C. After 5 days of incubation enzyme was extracted from each flask and assayed.Role of pH on xylanase production was studied as follows: Equal volume of (1ml) spore suspension was added in each flask containing 50 mg wheat bran with 70% moisture at 55°C at different pH i.e. 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 and 8.0 respectively. Effect of moisture content on enzyme activity was studied as follows: Fifty gm of wheat bran was taken in each 1000 ml conical flask and soaked with 20, 25, 30, 35, 40, 45 and 50 ml of distilled water to make 40%, 50%, 60%, 70%, 80%, 90% and 100% relative humidity respectively. Enzyme was extracted and assayed after 5 days of incubation. Ten miligram of different chemicals i.e. Thioglycolic acid, EDTA, SDS, HgCI2, CoCI2, MnCI2, , MgSO4, FeSO4, CaCI2, CUSO4, NaNO3, ZnCI2, Tyrosine and Aspartic acid was added separately in each flask containing wheat bran. Each sterilized flask was inoculated with equal volume of spore suspension and incubated at same culture condition for 5 days. Enzyme was then extracted and assayed (9,10). To determine the storage stability, crude enzyme was taken (30 ml) in screw cap test tube and kept at different temperature i.e. 0°C, 4°C, 15°C, 20°C, 30°C, 40°C, 50°C, 60°C and 70°C. Enzyme assay was done after six days interval up to 100 days. For enzyme assay, the dinitrosalicylic (DNS) method was followed Carboxymethyl cellulase (CMCase), xylanase, and polygalacturonase (POase) activities were measured with Na-CMC (Sigma, low viscosity) or xylan (Sigma, larch wood) or polygalacturonic acid-Na (Sigma) as substrate. The hydrolysis of these substrates was measured in a 0.15 M acetate buffer (pH 4.8) at 40°C. A 20 min. incubation time was used for substrate hydrolysis. Reducing sugars were determined calorimetrically with dinitrosalicylic reagent. The enzyme activities of CMCase, xylanase, and POase were calculated and expressed in international units (lU). One IU of enzyme is the amount of enzyme, which liberates one micro mole of reducing sugars per minute under the assay conditions.