The performance of an ultrafiltration hollow-fiber reactor, in which enzymatic synthesis of fructose 1,6-diphosphate (FDP) from glucose and enzymatic ATP regeneration are performed simultaneously, was analyzed theoretically. The reaction system consists of three-step synthetic reactions catalyzed by glucokinase (GB), phosphoglucose isomerase and phosphofructokinase, and the ATP regeneration reaction catalyzed by acetate kinase. Based on a simple analytical model developed previously in which the liquid flowing in a tube was assumed to be plug flow and the radial concentration gradients in the tubes and shell side space were both neglected, a computer program was developed to calculate the concentration profiles of all the components along the Row direction in the tubes and shell side space of the reactor. From the FDP concentrations at the reactor outlet calculated under various operational conditions, reactor performances such as the FDP yield and the ATP recycle number were determined. The calculation showed the interesting phenomenon that under some conditions the FDP yield was higher when GK concentration was lower.