Oat straw was treated with 1.5% and 3.0%. anhydrous ammonia of the weight of air dry oat straw in stack, and chemical composition and digestibilities were compared with untreated and anhydrous ammonia treated oat straw. Crude protein content of ammonia treated oat straw was increased 1.3-1.4 fold as compared with untreated oat straw. Neutral detergent fiber (NDF) was decreased significantly (p$lt;0.05) but acid detergent fiber(ADF) and cellulose content were not different from untreated and ammonia treated oat straw. Dry matter, crude protein, crude fiber and NFE digestibility of oat straw were increased significantly by ammonia treatment (p$lt;0.05). And, the ammoniation oat straw significantly improved the DCP and TDN at level 3% especially (p$lt;0.05). The feed intake of the oat straw was significantly increased by ammonia treatment (p $lt;0.05).