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For ethanol production from cellulosic biomass, an effective pretreatment step is required to reduce biomass recalcitrance by altering its chemical and structural features. Sodium hydroxide (NaOH) and lime (CaO) are two alkali reagents which have been extensively studied in chemical pretreatment of lignocellulosic biomass. However, high temperatures and pressures are routinely applied to effectively improve the digestibility of lignocellulose, which lead to the high cost of pretreatment. In previous studies, distinct properties of NaOH and CaO make it possible to manipulate these two alkali reagents to let them work together in lignocellulose pretreatment to reduce temperature, chemical loading, and residence time requirements. Corn Stover is considered as a potential feedstock for sugar production due to its great amount and easy access in the United States. In this research, NaOH and CaO are used together to pretreat corn stover at 50 oC. Three pretreatment parameters are studied: residence time, NaOH concentration, and CaO loading. The pretreatments were evaluated based on the sugar productions in the subsequent enzymatic hydrolysis. At recommended pretreatment conditions (9h, 0.75% NaOH, 0.05 g CaO g-1 raw biomass), the total reducing sugar yields was 544.0 mg g-1 raw biomass, at an overall carbohydrate conversion of 77.0%. However, compared with pretreatment at recommended conditions at room temperature, pretreatment at 50 oC may result in more energy and chemical input.