One-pot ethanol production from plant biomass (successive biomass pretreatment, enzymatic hydrolysis, and fermentation in a single vessel) is necessary for the practical production of second-generation bioethanol because multipot procedures require large energy inputs. One-pot ethanol production requires low-toxicity cellulose solvents, and liquid zwitterions are the most promising candidates. However, liquid zwitterions have complex synthetic procedures, which significantly increases the energy cost. Here, the applicability of low-toxic simple zwitterions was investigated from the viewpoint of pretreatment ability for one-pot ethanol production. In this study, a simple solid noncellulose dissolving zwitterion was able to reduce the crystallinity of microcrystalline cellulose. The pretreatment of cellulose was performed in a zwitterion/water mixture at 100 °C while removing water. The imidazolium cation and carboxylate anion are key structures for an efficient pretreatment. Cellulose pretreated with the solid zwitterion was susceptible to hydrolysis, and the hydrolysis efficiency was comparable to that of the liquid zwitterion, which dissolves cellulose. The simple solid zwitterion was also effective for biomass pretreatment. The zwitterion delignified as well as reduced crystallinity, resulting in the pretreatment of bagasse. The pretreatment ability for bagasse was comparable to that of liquid zwitterions.