Thermoascus aurantiacus was the most active cellulase producer of several thermphilic fungi tested. The optimum growth temperature for T. aurantiacus in liquid medium was 45° C and maximum cellulose production from filter paper occurred at 40° C The optimum temperatue for $-glucosidase and carboxymethylcellulase activity was 70° C; for filter paper degrading activity it was 65°C. Maximum activity was found at pH 5.0 for the filter paper degrading enzyme and Q-glucosidase and pH 4.3 for carboxymethylcellulase activity.