A hollow-fiber hemodialyzer with alpha-amylase immobilized on the lumen and outer surface of hollow fibers was employed to hydrolyze the high-concentration starch slurry. The viscous starch slurry was first hydrolyzed in the shell side of the hollow-fiber reactor, and the unconverted starch was further hydrolyzed as the slurry circulated through the narrow lumen of hollow fibers. The reactor retained 65% of its initial activity after a 30-batch reaction at 65 degrees C. Starch slurry of 30% (wt/vol) can be hydrolyzed without any difficulties by the hollow-fiber reactor. In continuous operation, a starch hydrolysate of dextrose equivalent 12% was obtained at mean residence time of 9.5 min.