Rice straw was treated with 3.0% anhydrous ammonia and 1.5% and 3.0% aquous ammonia of the weight of air dry rice straw in a wire mesh silo and stack, and chemical composition and in vitro digestibilities were compared with anhydrous and aquous ammonia treated rice straw. Crude protein content of ammonia treated rice straw was increased by 2-3 fold as compared with untreated rice straw. Neutral detergent fiber (NDF) was decreased significantly (p $lt; 0.05) but acid detergent fiber (ADF) and cellulose content were not different from untreated and ammonia treated rice straw. Chemical composition of rice straw treated with anhydrous and aquous ammonia was not different. Of the total nitrogen added as 3% anhydrous and 3% aquous ammonia, 25.1-38.9% and 26.3-58.3% were retained in the rice straw and 61.1-74.9% and 41.7-73.7% were lost in this experiment. Dry matter, NDF, ADF and cellulose digestibilities of rice straw were increased significantly by ammonia treatment (p $lt; 0.01) and improvement of digestibility was higher in rice straw treated with aquous ammonia as compared with anhydrous ammonia. Digestibility of rice straw treated with 3.0% aquous ammonia was higher than that with 1.5% aquous ammonia (p $lt;0.05).