In recent years enzymes have been used in increasing quantities by the animal feed supply industry for the production of both monogastric and ruminant animal feeds. The use of enzymes provides an effective biological way of improving the nutritional quality of cellulose and hemicellulose based feeds (Viikari et al., 1993, Millet et al., 1976). The present study involved the isolation and purification of an endoglucanase produced by Thermoascus aurantiacus with an emphasis on characterising heat stable enzymes which would have an obvious advantage in industrial processes, especially those involving pelleting of the final diet.