The hydrolysis of starch by the catalysis of α-amylase was monitored by a network analysis method, resulting in a new method for determination of α-amylase with a Bulk Acoustic Wave (BAW) viscosity sensor. The response of the sensor to the viscosity and density change of this process are measured. The frequency shift during a certain time interval is linearly related to the concentration of α-amylase in the range of 20-500 U.L−1. This method is simple, as no extra reagent such as chromogen or fluorescein is needed. It is fit for the continuous monitoring of the catalytic process and it may also be used to study the dynamics of the process.