The relative proportions and potentially digestible dry matter contents of corn grain, corn cob and corn stover, and improvement of digestibilities of corn cob and corn stover by alkali treatment were estimated in vitro method and the result were summarized as follows. 1. The relative proportion, of corn grain, corn cob and corn stover of whole corn plant on a dry matter basin were 39.3%, 11.1% and 49.6%, respectively. 2. Corn grain had the highest amount of crude protein(9.7%) followed icy corn stover(6.4%) and corn cob(4.6%). Corn cob had the highest amount of cell wall constituent(CWC) (82.6%) followed by corn stover(68.4%)and corn grain (23.2%). Corn cob had higher amount of CWC, acid detergent fiber (ADF) and cellulose but lower amount of lignin than corn .Mover. 3. Potentially digestible dry matter (PDDM) contents of corn grain, corn cob and corn Mover were 95.5%, 80.5% and 68.8%, respectively. Whole corn plant contained 80.4%, of PDDM, which were consisted of 37.5%, of corn grain, 8.9% of corn cob and 34.0% of corn stower. 4. Dry matter digestibilities of corn grant, corn cob and corn slower were 79.9% 66.5% and 60.0%, respectively. Alkali treatment of corn cob and corn stover improved significantly dry matter, CWC, ADF and cellulose digestibilitiea (p$lt;0.01) and improvements were much higher in corn cob treated at 100℃ for 1 hour than 23℃ for 24hour(p$lt;0.01), but in corn slower there were no significant differences between treatment temperature.