The present study was conducted to investigate the relationship between the feed value and fermentation quality of silage evaluated by the rapid titration method. The buffer index value was determined from the amount of 0.1N NaOH consumed in titration of each 0.5 pH step. Thirty four samples of com silage which had been collected from farms were assessed by deriving the buffer index curve. The silages were also analysed by the routine chemical methods for organic acids, dry matter, crude protein, crude fiber and ammonia-nitrogen. Degradability of silage dry matter was measured by incubating samples in nylon bags suspended in the rumen. Duplicated bags were removed at 12 and 24h postincubation. Each of fourteen silages had a same peak position at pH 4.0 on index curve (B type) and showed the characteristics of lactic acid fermentation. Twenty silages with a same position peak at pH 4.5 (C type) were moderately well preserved. The B type silages were higher in dry matter content and lower in crude protein and crude fiber contents compared to the C type silages. It should be noted that the B type silages were ensiled at more profitable maturation stage than the C type silages. Fourteen silages which had been selected randomly were deteriorated in aerobic phase to obtain the spoiled silages. By the results of titrating those extract juice, all of the silages had the same peak positions at pH 5.0 on each buffer index curve (D type) and showed significantly (P$lt;0.001) lower dry matter degarability than the B and C types. The results indicate that feed values of silage can be predicted by the rapid titration method.