Effects of alkali treatment on the digestibilities and rates and extends of fermentation of dry matter of rice straw, barely straw were determined in vitro. Dry matter digestibilities of rice straw, barley straw markedly increased with increasing levels of NaOH treatment and the extent of increase was much higher at 100 ℃ for 1 hour treatment than at room temperature for 24 hours treatment. Dry matter digestibility of untreated rice straw was 38.53% and of treated rice straw with 4.8% NaOH were 57.29%, 79.24% at room temperature for 24 hours and 65.32%, 85.19% at 100℃ for 1 hour treatment, respectively. Dry matter digestibility of untreated barley straw was 37.39% and of treated barley straw with 4,8% NaOH were 59.15%, 77.09% at room temperature for 24 hours and 62.20%, 79.53% at 100℃ for 1 hour treatment, respectively. Fermentation rate constants and fermentation time of dry matter of untreated rice straw were 0.00741 hr^(-1), 135 hr and of treated rice straw with 4,8% NaOH were 0.01065 hr^(-1), 0.01919 hr^(-1) and 94 hr, 52 hr at room temperature for 24 hours treatment and 0.01919 hr^(-1), 0.02376 hr^(-1) and 52 hr, 42 hr at 100℃ for 1 hour treatment, respectively. Fermentation rate constants and fermentation time of dry matter of untreated barley straw were 0.00636 hr^(-1), 157 hr and of treated barley straw with 4,8% NaOH were 0.0134 hr^(-1), 0.02321 hr^(-1) and 75 hr, 43 hr at room temperature for 24 hours and 0.01324 hr^(-1), 0.02217 hr^(-1) and 76 hr, 45 hr at 100 ℃ for 1 hour treatment, respectively.