Breast cancer is the most common type of cancer among women. Cyclin D dependent kinases inhibitors have been approved based on extensive clinical trials that were carried out in the last ten years. They are indicated in treatment for locally progressed or metastatic breast cancer, which is hormone positive, HER2 negative, and are used, among other, in combination with fulvestrant. In order to secure that the following combination is effective and safe for patients, it is necessary to develop a unique analytical method which can reliably determine their blood concentration. Capillary electrophoresis techniques are becoming more and more used in today's drug quality control, but also drug detection in biological tissue. The aim of this research was to develop a new capillary electrophoresis technique which will be able to detect and quantify fulvestrant, palbociclib, ribociclib and abemaciclib in blood samples of patients in the purpose of therapeutic drug monitoring and in order to apply appropriate therapy individualisation. As a potential method for its analysis, micellar electrokinetic chromatography has been chosen. Capillary that was used is made of extracted quartz with an inner diameter of 50 m and total length 40 cm. The samples were injected in the capillary for 5 seconds, under the pressure of 50 mbar and temperature of 25 degrees Celsius. The results were observed at the wavelength of 210 nm. In order to form the micelles, surfactant SDS was added in the concentration of 60 mM. Beside surfactant concentration, other parameters that resulted with the best selectivity and sensitivity are borate buffer in the concentration of 25 mM, addition of acetonitrile to buffer in the fraction of 10 % and applied voltage of 28 kV.