This experiment was conducted to determine the effect of 3% ammonia treatment of rice straw on the chemical composition, in vitro digestibilities. fermentation time, and fermentation rate. And incubation time was carried out for 12, 24, 48, 72, 96hr at given incubation time by in vitro batch culture method. The results were summarized as follows: 1. Crude protein content of 3% ammonia treated rice straw, compared with 5.34%, in untreated rice straw was 9.55% which unexpected showed increase of 178.84%. Compared with untreated rice straw. NDF and ADF contents of ammonia treated rice straw were decreased by 10.45%, 10.53%. respectively. In comparison untreated and ammonia treated rice straw, contents of crude fiber, crude ash, and ether extract were not changed. 2. Retained ammonia nitrogen content in ammonia treated rice straw was 27.53%. 3. In vitro digestibilities of dry matter, NDF, ADF and cellulose were increased significantly by the ammonia treatment(p $lt;0.05). 4. In comparison untreated and ammonia treated rice straw, crude protein digestibilities of ammonia treated rice straw(24.02, 36.28, 60.29, 69.95, and 73.63%) at given incubation time divided by 12, 24, 48, 72, 96 hours were much higher than untreated rice straw(16.90, 21.27, 33.43, 49.31, and 49.28%). respectively. 5. Dry matter fermentation of untreated rice straw required 160.26 hours. which means dry matter fermented 0.62% per hour. Dry matter fermentation of ammonia treated rice straw required 99.44 hours(1.01%/hour). Fermentation rates of NDF, ADF, cellulose were showed the highest increase in ammonia treated rice straw.