This experiment was conducted to investigate the effects of formic acid addition(0.2%, 0.4% and 0.6% levels) and wilt on the quality of barley silage in accordance with growth stage, and pH and organic acid content were also analyzed. The results obtained were summarized as follows: 1. In the chemical composition of raw barley, moisture, crude protein and crude fat were decreased with advancing the maturity, but crude fiber and NFE were reversely increased. The water soluble carbohydrate content was 12.7% in the milky stage and was the highest among growth stages. It was also decreased with advancing the maturity. 2. The crude protein content of barley silage was increased by addition of formic acid and wilt treatment. ADF and NDF content were increased with advancing the maturity. ADF content was decreased in proportion to addition of formic acid. 3. pH tended to a little increase with advancing the maturity and was a little low by increasing the level of formic acid. The lactic acid content was the highest in the milky stage and in the 0.6% formic acid addition. Based on the above results, it would be suggested that the superior quality of barley can be produced from the heading stage to the milky stage from 0.4% to 0.6% in the level of formic acid for the making of barley silage.