A low-cost and sensitive amperometric biosensor was developed for the determination of alpha-amylase activity. The biosensor was constructed by immobilizing glucose oxidase-gelatin via glutaraldehyde on the Au electrode surface. Measurements were carried out chronoamperometrically at -0.7 V. Several parameters such as glucose oxidase activity, gelatin amount, and glutaraldehyde percentage for cross-linking were optimized. Optimum pH, optimum temperature, repeatability, and storage stabilities of the biosensor were identified. Under the optimum experimental conditions, a linear calibration curve was obtained for alpha-amylase between 0.819 and 13.110 U/ml. Sample analyses were carried out by detecting alpha-amylase activities in baker's yeast samples.