The enzyme activity of immobilized β-amylase carried on active carbon and the reaction kinetics for hydrolysis of potatostarch catalyzed by the enzyme have been investigated. A kinetics model based on the overall reaction has been suggested and a reaction coefficient as a new parameter introduced. All of the kinetics parameters involved in the model, including the reaction coefficient, reaction order rate constant as well as the maximum reaction rate etc. at different temperatures have been obtained by using the modified Quasi-Newton optimization technique. The enzyme activity of immobilized β-amylase carried on active carbon and the reaction kinetics for hydrolysis of potatostarch catalyzed by the enzyme have been investigated. A kinetics model based on the overall reaction has been suggested and a reaction coefficient as a new parameter introduced. All of the kinetics parameters involved in the model, including the reaction coefficient, reaction order rate constant as well as the maximum reaction rate etc. at different temperatures have been obtained by using the modified Quasi-Newton optimization technique.