A solution of α-amylase liquefied cassava starch, 30% (w/v), was saccharified with amyloglucosidase at 45°C, pH 4.5, in a batch reactor in the presence and absence of added glucose. Reactor conversion results were modeled with a multisubstrate model that considers intermediate dextrins of starch hydrolysis, reversibility of some reactions, substrate and product inhibition, and competition among dextrins and isomaltose formation. Kinetic parameters were obtained from initial velocity saccharification tests at different starch concentrations and from the literature. The model can represent well the saccharification of cassava starch even in the presence of a great excess of glucose (100 g/L), added to test its capability.