PROBLEM TO BE SOLVED: To provide a novel cellobionic acid phosphorylase and a production method of acidic &bgr;-glucosyl disaccharide using the same, that enable production of cellobionic acid efficiently from inexpensive materials by an enzymatic synthesis method.SOLUTION: Acidic &bgr;-glucosyl disaccharide is produced by oligosaccharide synthesis reaction catalyzed by a newly discovered cellobionic acid phosphorylase, using α-glucose-1-phosphate and gluconic acid or glucuronic acid as starting materials. Further, α-glucose-1-phosphate is produced by combination of carbohydrate-processing phosphorolytic enzyme and carbohydrate as its ground substance, and at the same time, acidic &bgr;-glucosyl disaccharide is produced by an oligosaccharide synthesis reaction catalyzed by the discovered novel cellobionic acid phosphorylase.
