A series of methylcellulose (MC) samples were successfully synthesized using dimethyl sulphate (DMS) as a methylation reagent in 7 wt% NaOH/12 wt% urea aqueous solution through controlling the reaction conditions. The MC samples were characterized with H-1 and C-13 NMR, gas chromatography (GC), ultraviolet spectroscopy, viscometry and solubility measurement. Analysis of GC showed that there were no unsubstituted anhydroglucose units (AGU) and few completely substituted AGU along the molecular chains of the MC samples, and there was a uniform distribution of methyl substitution along the MC molecular chains. The stability of 7 wt% NaOH/12 wt% urea solution for the methylation of cellulose was investigated for the first time. The results showed 2 wt% cellulose solution in the 7 wt% NaOH/12 wt% urea solvent was almost stable at room temperature, and little decomposition of the cellulose molecular chains occurred during the methylation reaction.