A novel cyclic acetal derivative of sucrose, 4,6-O-isopropylidenesucrose, is prepared by treating sucrose with 2,2-dimethoxypropane in N,N-dimethylformamide, in the presence of p-toluenesulphonic acid, suitably at room temperature. The product is conveniently isolated in the form of its hexa-acetate or hexabenzoate, by treatment with acetic anhydride or benzoyl chloride, respectively, in pyridine. The resulting compounds are valuable as synthetic intermediates and in conformational investigations.