The continuous production of Glucose-1-phosphate (G-1-P) using immobilized potato phosphorylase was investigated. Potato phosphorylase was immobilized on a strongly basic anion-exchange resin, HPA-25 through contact of the resin with potato juice or wastewater of a potato-starch factory. The immobilization was highly selective for phosphorylase among proteins contained in potato juice and the wastewater. The immobilized phosphorylase could be used for the continuous G-1-P production over one year without significant deactivation. By using a 100-L column reactor packed with immobilized phosphorylase of 14.1 U.mL-carrier(-1) at the superficial linear velocity of 0.034 m.h(-1) and the space velocity of 3.1 x 10(-9) m(3).U-1.h(-1), 185 mM G-1-P, which is the maximum concentration potentially expected from 516 mM dextrin and 2000 mM phosphate, was continuously produced.