This thesis presents a process for assessing and improving the precision of CNC machine tools. The precision of CNC machine tools is directly correlated with the precision of machined products, which is defined by the positional accuracy and repeatability of the machine tools. The precision of machine tools is usually verified in some periodic time units or when a change in geometric precision of the machined products is detected. This study comprises a comprehensive inventory of steps in checking and improving the precision of CNC lathes. The initial condition of such machines is presented, and based on that, a procedure for improving the accuracy and robustness of achieving tool-making precision is designed (complete cleaning of the CNC lathe, including the replacement of old emulsion with a new one, calibration of the removable measuring hand for cutting tool offset measurement, verification of the axis and quill working precision and the corresponding correction of the controller). The procedure was experimentally tested on a Mori Seiki SL-153 lathe. As a result, the restoration of the machine tool from the initial accuracy class of 0.15 mm to a final accuracy of less than 0.01 mm was obtained.