In order to obtain a good microorganism capable of degrading microcrystaline cellulose (avicel), the screening test was carried out from soil and brown-rot wood. 8 strains which had good avicel-hydrolyzing activity were isolated. Among them, HK 47 which exhibited the highest avicel hydrolyzing activity was identified as Trichoderma sp. HK 47. Maximum avicel-hydrolyzing enzyme production from Trichoderma sp. HK 47 was obtained with the optimum medium contained carboxymethylcellulose 1.5% as carbon source, NaNO_3 0.75% as nitrogen source, KH_2PO_4 0.5%, MgSO_4·7H_2O 0.1%, Tween 80 0.005% (V/V) during stationary cultivation at pH 6.0, 30℃. In this case, the production of avicel-hydrolyzing enzyme was 0.028U/㎖.