Abstract: Trichoderma koningi Oudemans (3.2064), a cellulose-decomposing fungus isolated from rotten corn kernel, has been screened from more than 100 strains of fungi belonging to the genera of Trichoderma, Chaetomium, Stachybotrys and Myrothecium. Attempts have been made to study the physiology of T. koningi with reference to its practical application to the fermentation of industrial and agricultural by-products as well as wild plant materials. The results were obtained as follows. The decomposition ratio of straw cellulose by T. koningi was 32% and 50% for 3 days and 9 days respectively. The saccharifying ability of the fungus on wheat straw is rather high and the reducing sugar was determined to be 29 mg/g per hour. Evidence have been obtained to show that T. koningi may produce antibiotics resembling viridin and gliotoxin, both in liquid medium and mycelia. Such Trichodermafeeds are non-poisonous or harmless when fed to animals after bolling. Mycelial growth has been found to occur between 15–40 ℃, and to cease at 10 ℃ and 45 ℃, the temperature for the most rapid mycelial growth being about 36 ℃. Under the conditions in forage fermentation, the accumulative temperatures for spore germination, mycelial development and sporulation have been found to be 61, 153 and 380 hourdegree (C.) respectively. The relative humidity most favorable for mycelial growth is 98%, and the growth ceases when the relative humidity is below 92%. The pH range favorable for mycelial growth on liquid medium is from 4.0 to 7.5, the optimum being about pH 6.0, and no growth occurs at pH 2.5 and pH 9.0. T. koningi is capable of utilizing d(+)mannose, d(+)glucose, d(+)xylose, cellubiose, dextrin, maltose, fructosan and fructose; glycerin, fumaric acid, puruvic acid and d(+) galactose rank next in utility; soluble starch, d(-)arabinose, d(-)erythrose, lactose, suc- rose, raffinose, d(-)ribose, dihydroxyacetone, agaragar and L-rhamnose are poor carbon sources for this microorganism. Among these compounds, fructosan and sucrose are very effective for sporulation. The fungus is capable of utilizing both organic and inorganic sources of nitrogen, but the former seems to be better for assimilation. Among amino acids, L-glutamic acid and L-tryptophan are the most favorable for mycelial growth, on the contrary, the aromatic acids and the amino acid containing sulphur are least assimilable as nitrogen sources for this fungus. L-Glutamic acid, asparagin and DL-valine are the most favorable for spore production.