The following thesis examines measurment of the tool wear, which is caused by several wear mechanisms. Different types of tool wear and tool fracture are presented in theoretical part of the thesis. It is discussed, how tool damage can be prevented in the beginning phase of the milling process. Different wear mechanisms and their correlation with cutting speed, mechanical properties and temperature in the cutting zone are explained in detail. Structure and operation of the measurment system are described in the main part of the thesis.