Loss of energy potential during storage is a significant consideration when using crop residues for bioenergy production. However, previous studies about biomass storage only reported dry matter loss and composition change, but not the direct effects on bioenergy production. This study investigated the changes in chemical composition, enzymatic digestibility, and methane yield of corn stover after one-year outdoor dry bale storage under covered and uncovered conditions. The contents of easily degradable components, including extractives and hemicellulose, decreased by about 20%-50%, while the contents of cellulose and lignin did not change significantly. The methane yields of corn stover after one-year covered or uncovered storage declined by 13.2% and 22.7%, respectively, partially due to the decrease of cellulose degradability and the losses of hemicellulose and extractives. Increasing particle size from 1 mm to 12.7 mm reduced the methane yield of the stored corn stover by up to 26.4%. The modified Gompertz model suggested that both storage conditions and particle size affected methane yield, maximum methane production rate, and lag phase time of anaerobic digestion (AD) of corn stover. The information reported in this paper can provide important information for economic analysis and life cycle analysis of AD of corn stover. (C) 2018 Elsevier Ltd. All rights reserved.