Within this graduate thesis, a plan of experiments whose purpose was to examine the influence of process parameters on the size and charge of micro particles containing melatonin prepared using the spray drying technique was successfully carried out and evaluated. Knowing the size of the raw materials as well as the size of particles in the drug product is important for the therapeutic effect, stability, shaping and storage of the medication. The particles' surface charge influences the stability of the sample, which is manifested in a greater resilience to flocculation and aggregation of the particles. In order to design the experiment plan, and for the statistical analysis of the data acquired from the analysis of the micro particles containing melatonin the JMP program was used. The factors with the biggest influence on the target parameter were determined by the statistical analysis. By changing the process parameters of the pump speed (20-40 %), the lipid-chitosan ratio (31,25-62,5) and the air temperature (110-125 °C), 13 micro particle samples which differed in size and Z-potential values were obtained. Using the method of linear regression did not result in a curve that showed the linear relation between the predicted and obtained particle sizes. Therefore, it was determined that in the tested lipid-chitosan ratio, pump speed and drying temperature there were no significant changes in the size of the prepared particles. The mathematical analysis of the JMP program determined that the lipid-chitosan ratio has the biggest influence on the Z-potential value, which was expected seeing as chitosan carries a positive, whereas the lipid component carries a negative charge. The air temperature has a moderate influence on the Z-potential, while the speed pump has a weak influence.