A method for determination of lysozyme with a Bulk Acoustic Wave (BAW) viscosity sensor is presented. It is based on the bacteriolytic action of lysozyme on Micrococcus lysodeikeicus (M. lysodeikeicus) and the response of the sensor to the viscosity and density change of this process. There was a good correlation between the frequency shift and the concentration of lysozyme in the range 10–100 μg/ml. The content of lysozyme in human saliva was determined by this method and the results obtained were in good agreement with those from the conventional turbidimetric method. This method has an advantage over the conventional turbidimetric method in that the amount of sample needed is smaller, the procedure is simpler and the concentration range of the bacterium suspension which can be used in the detection was extended.