The effects of operating conditions on the enzymatic hydrolysis of corn starch were investigated. A commercial alpha-amylase produced by Bacillus sp. was used for the hydrolysis experiments. The degree of starch hydrolysis (%) and residual alpha-amylase activity (%) was investigated versus process variables, including pH, temperature, viscosity, impeller speed, processing time and some materials added such as hydrolysate, maltose, glucose, ethanol and CaCl2 using a stirred batch reactor. The mathematical models depending on the operating conditions were also derived using the experimental data of residual starch concentration. Some inactivation models were tested to determine the relationship between process variables and enzyme stability during the hydrolysis process. (C) 2003 Elsevier Ltd. All rights reserved.