Cellobiose was enzymatically synthesized from starch using two phosphorylases. Under the presence of 1 m Pi (inorganic phosphate), glucan phosphorylase converted 40% of glucose residues in the starch molecule into G1P (glucose-1-phosphate). By electrodialysis fitted with an ion exchange membrane having molecular weight cutoff of 100, Pi was effectively dialyzed out and G1P was recovered with 80% yield. G1P and glucose were incubated with cellobiose phosphorylase in the presence of magnesium acetate at an alkaline condition. Inorganic phosphate coformed with cellobiose was immediately removed as insoluble magnesium ammonium phosphate and 85% of added G1P was converted into cellobiose. On the whole, cellobiose was produced with 60% yield from G1P and, at least, 23.7% yield from starch.