A mathematical model for direct alcohol fermentation from starch was proposed using an amylase-producing recombinant yeast, Saccharomyces cerevisiae SR93. This model consisted of the reaction rate equations for glucoamylase synthesis in the recombinant yeast, starch degradation by a glucoamylase, cell growth, production of glucose, and production of ethanol. The rate of glucoamylase synthesis was expressed on the basis of the diauxic growth model that represents catabolite repression and enzyme induction. The rate of starch degradation was expressed on the basis of the enzymatic hydrolysis model representing the change of structure resulting from starch degradation. The calculated values were in satisfactory agreement with the experimental data in a batch culture of direct alcohol fermentation from starch using S cerevisiae SR93. Furthermore, the calculated values obtained by changing only one parameter concerning the synthesis rate of glucoamylase were in satisfactory agreement with the experimental data using another recombinant yeast, S cerevisiae SR96. (C) 2003 Society of Chemical Industry.