The pretreatment efficiency of weight ratios ranging from 0 to 10 of the ionic liquid, cholinum IL, to bamboo powder was investigated. An IL/biomass ratio of 3 g/g was critical to obtain a cellulose saccharification ratio of 80%. At this ratio, the treated bamboo powder remained as a solid. The solid-state pretreatment required a minimum amount of cholinium IL, which could reduce the cost of IL-assisted pretreatment and reduce the amount of wastewater generated in the process. (C) 2012 Elsevier Ltd. All rights reserved.