Considering the growing incidence of breast cancer in our population, there is a need to develop an analytical method that can be used in therapeutic drug monitoring to enhance the success of therapy. The goal of this research was to develop a new capillary electrophoresis method so that any of the observed drugs from the ciclib group – abemaciclib, ribociclib or palbociclib could be detected or quantified in a simple, fast and accurate way. The technique used is zone capillary electrophoresis. This analysis was performed on a 32,5 cm long capillary of extracted quartz with an inner diameter of 50 μm. The samples were injected into the capillary under a pressure of 50 mbar, at a temperature of 25 °C for 6 seconds. A wavelength of 320 nm was used. The following parameters were optimized through the study - type and pH of the buffer, buffer concentration, voltage, temperature and flushing conditions. Their influence on the analysis time, peak area, number of theoretical plates and peak symmetry was monitored. The optimal values found included 50 mM phosphate buffer, voltage 27.5 kV and temperature 30 °C. For optimal flushing conditions, it was chosen to flush at the beginning of the day for 10 minutes with 10% phosphoric acid, 10 minutes with ultrapure water and 20 minutes with the working buffer, and at the end of the day 20 minutes with ultrapure water and to precondition for 5 minutes between measurements with the working buffer. It turned out that for the successful and reproducible analysis, the working conditions with the citat buffer at pH 3.17, buffer concentration 113 mM, temperature 25 °C, voltage 20 kV and pH 4.11, buffer concentration 35 mM, temperature 25 °C and voltage 25 kV were also sufficient.