The optimum condition, iterative usage and activity change of α-amylase which was immobilized on insoluble carrier polyacrylonitrile(PAN) was estimated The emulsion Polymerized PAN was Partially imidoesterified with anhydrous methanol and dry HCI gas, on which α-amylase was immobilized in Phosphate buffer solution. The activity and its stability of immobilized α-amylase was investigated at various pH, temperature and time with a batch and a continuous system. From these results, the activity of immobilized α-amylase was slightly decreased than that of free α-amylase. The optimum condition of immobilized α-amylase was obtained at PH 7, 40℃. The stability of immobilized α-amylase decreased until 4∼5 times usage, but stabilized thereafter. To estimate the dynamic properties of diffusion resistance of substrate, apparent Michaelis constant(K''m) was calculated by using the Bar-Eli & Katchalski equation. The K''m was increased after iterative usage maybe due to the decrease of diffusion velocity. The K''m was also increased on decreasing flow rate and therefore on increasing contact time.