In this report, a-Amylase originating from Bacillus subtilis (liquefying type) was immobilized on partially imidoesterized polyacrylonitrile (PAN) by covalent bonding. For the preparation of immobilized a-amylase, which has a high activity and high stability to repeated use, the optimum conditions for the preparation reaction were investigated. The optimum conditions for the preparation reaction were quantified on the basis of the enzymatic activity, the preservation of the activity during repeated use in batch process and the protein content on the support. Furthermore, enzymatic properties of immobilized a-amylase prepared at optimum conditions were compared with the native enzyme. The optimum temperature and reaction time for the imidoesterification reaction were 30°C and 6 h, respectively, whereas those of the amidination reaction were 30-40°C and more than 3 h, respectively; the optimum pH range was 9-10. Immobilized aamylase prepared at the optimum conditions was very stable against the repeated use and had more than 90% of relative activity to the first use after the tenth procedure. The initial reaction rate of immobilized a-amylase was lower than native a-amylase, but same amount of reducing sugars were produced after the reaction passed for more than 90 min. The immobilized a-amylase was less stable at the high temperature and the more basic media. However, after long incubation time, immobilized a-amylase was more stable than the native enzyme in exposure to heat and a strong base.