1,1,3,3-tetramethylguanidinium hydrogen sulphate (TMG·HSO₄) ionic liquid was used for the hydrolysis of cellulose using water enriched with carbon dioxide as the reaction media. The addition of carbon dioxide enhanced the reaction rates significantly and afforded glucose and total reducing sugars in 26 and 72% yields, respectively. The addition of carbon dioxide might play a dual role, it reduces the viscosity of the medium for better mass transfer and also reacts with water to give carbonic acid which subsequently dissociates to the hydronium ion and enhances the acidity of the medium. The developed ionic liquid was easily recovered and reused for a subsequent four runs without any significant change in the catalytic efficiency.