Roughage feeds were produced by physical and chemical treatments from Hyun-aspen (Populus alba × P. glandulosa) . The objectives of this work were to find proper methods and conditions for the treatment of Hyun-aspen by analyzing the compositional change and digestibility, and to make single cell protein from acid extracted solution of Hyun-aspen by fermentation. The results of this work were as follows : 1. The proper condition for autohydrolysis of Hyun-aspen chips were 160 C and 30 minutes in a autoclave. The yield of potential feed from original material and digestibility were 91.3% and 38.9%. respectively. The sugar Concentration of extracted solution, the recovery rate of sugar and the concentration of phenol were 0.4%, 2.4% and 0.1%, respectively. 2. Cooking the aspen chips at 145℃ for 50 minutes in the presence of 1% sulfuric acid was the best condition, The dry matter yield and the digestibility were 86.4% and 37.9%. respectively. The sugar concentration of extracted solution, the recovery rate of sugar and the concentration of phenol were 0.8%, 4.2% and 0.2%, respectively. 3. Aspen chips treated with 6% NaOH and cooked at 160℃ for 10 minutes of various alkali treatments were considered as best roughage. The dry matter yield and the digestibility were 85.2% and 41.6%, respectively. The concentration of sugar, the recovery rate of sugar and the concentration of phenol were 0.9%, 2.0% and 0.2%, respectively. 4. The method of steaming-defibration gave the best producing rate of feed-stuffs when the chips were steamed (9㎏/㎠ under the pressure) for 10 minutes. The yield and the digestibility of feedstuffs were 84.2 and 38.1%, respectively. 5. For defibration of the chip by explosion, the proper condition was steamed under the pressure (20㎏/㎠) for 4 minutes, The yield and the digestibility of feedstuffs were 93.9%, and 68.1%, respectively, The feedstuffs produced under these conditions had higher nutritional quality than rice straw and this method was considered as the best for making feedstuffs from Hyun-aspen chip. The physical properties of the feedstuffs were investigated by a light microscope and a TEM. The feedstuffs produced under the low pressure (20 ㎏/㎠) still maintained the structure of fibers, However, the feedstuffs produced under the high pressure (28㎏/㎠`) resulted in higher defibration than these prepared under the low pressure. The highly defibrated feedstuffs recombined with solublized lignin, The crystallinity of feedstuffs was increased by 10% and micelle width increased double after treatment. 6. Candida tropicalis NCYC 978 was cultured in extracted solutions of Hyun-aspen by chemical treatment after it was refined. The cell recovery rates were 13-19% depending on the culture conditions. The best growing condition was obtained by adding Ca-pantothenate (5㎎/ℓ) in culture medium which had pH 4.6 and 0.3% (NH₂)₂CO as nitrogen source. The yeast contained high quantity of cell-protein and grew fast in this medium.