A method of separating a saccharide from an aqueous product solution of the cellulose hydrolysis process is provided. The aqueous product solution comprises a saccharide and a cellulose swelling agent. The cellulose swelling agent is zinc chloride, magnesium chloride or a combination thereof. The method comprises the following steps in the given order: (a) adding a first tertiary amine and an optional first organic solvent to the aqueous product solution to provide a mixture; (b) performing a solid-liquid separation to obtain a solution from the mixture; and (c) performing a liquid-liquid extraction by adding a second tertiary amine and a second organic solvent to the solution, and then removing the organic phase and collecting the aqueous phase, wherein the first tertiary amine and the second tertiary amine are the same or different, and the first organic solvent and the second organic solvent are the same or different.