The study aimed to explore the crystallinity and crystalline structure of alkaline pretreated cellulose. The enzymatic hydrolysis followed by pretreatment was conducted for measuring the efficiency of sugar conversion. For cellulose I beta dominated samples, alkaline pretreatment (< 8 wt%) caused increased cellulose crystallinity and depolymerized hemicelluloses, that were superimposed to affect the enzymatic conversion to glucose. Varying crystallite sizes and lattice spacings indicated the separation of cellulose crystals during mercerization (8-12 wt% NaOH). Completion of mercerization was proved under higher alkaline concentration (14-18 wt% NaOH), leading to distortion of crystalline cellulose to some extent. Cellulose II crystallinity showed a stimulative impact on enzymatic hydrolysis due to the weakened hydrophobic interactions within cellulose chains. The current study may provide innovative explanations for enhanced enzymatic digestibility of alkaline pretreated lignocellulosic materials. (C) 2016 Elsevier Ltd. All rights reserved.