Transient responses of immobilized enzyme reactors were obtained by solving coupled governing equations for core-shell catalytic pellets. The morphology of the pellets was assumed as sphere, cylinder, and slab-type particles having inert cores. Nonlinear reaction-diffusion equations of batch-mode reaction systems were solved by finite element method using commercial software, COMSOL Multiphysics, to investigate the effect of adjustable parameters such as thickness of inert core, Biot number, and the amount of pellets as well as reaction parameters of Michaelis- Menten kinetics. Modeling of CSTR was also carried out and the results were compared with the transient response of batch reactor by adjusting retention time during numerical calculations, reflecting deactivation of enzyme as timedependent rate constant. For both types of reactors, spherical pellets were the most advantageous for reduction of reactant concentration with relatively smaller effect of the thickness of inert core, compared to other types of pellets. Additionally, a number of connected CSTRs were assumed for approximate analysis of fixed bed reactor, of which the behavior became close to a simple CSTR with increasing axial dispersion.