AbstractHydrothermal pretreatment of corncobs in aqueous media under non-isothermal conditions is an effective means for solubilizing hemicellulose fractions and improving cellulose hydrolysis. The effects of a range of pretreatment severities (temperatures of 170 to 230 °C) on the conversion of corncobs into fermentable sugars were examined. The major differences between the conversions of untreated and pretreated corncobs were the dissolution of hemicelluloses into the prehydrolyzate and the partial removal and relocation of lignin on the external surface of biomass particles (in the form of recondensed droplets) in the pretreated corncobs. Hemicellulose dissolution increased with pretreatment temperature. The maximum sugar recovery (272.3 g/kg raw material) and the minimum accumulation of inhibitory compounds in the prehydrolyzate were observed following treatment at 190 °C. While the fibrils of the untreated raw material remained largely intact, serious disruption of the cell wall was observed in SEM images of the surfaces of pretreated samples. Accordingly, the cellulose digestibilities of residues increased from 26.8% for the raw material to almost 100% for the 190 °C-treated sample. It was concluded that low severity hydrothermal pretreatment can be successfully applied to corncobs to obtain high cellulose digestibility while operating at low enzyme charges.