Straw, hay, and silage from annual cereal crops are potential biomass feedstocks for ethanol production in Montana. However, the storage, processing, and conversion technologies for various biomass feedstocks have not been well developed. Straws and hays are different plant materials and they contain different soluble and structural carbohydrates. The objectives of this study were: 1) to measure soluble and structural carbohydrates in straws and hays, 2) to determine if ensiling and enzyme-added ensiling can enhance the structural carbohydrate conversion to sugars. Soluble sugar content was as much as 19% for winter cereal hays, but the soluble sugar content was only 3% for straws. Cellulose and lignin contents were greater in straws than in hays. Cellulose content was about 40% for straws and 30% for hays; lignin content was about 10% for straws and 5% for hays. Hemicellulose content was about 21% for straws and hays. Ensiling enhanced sugar conversion and enzyme-added ensiling further increased the conversion rate. Sugar yield after enzymatic hydrolysis was 23 to 31% for hays, 31 to 45% for non-enzyme-added silages, and 49 to 59% for enzyme-added silage in this study. Ensiling with or without enzyme added had little effect on sugar conversion of straws.