Quetiapine is a dibenzothiazepine antipsyhotic medicine of second-generation. Today, it is one of the most prescribed drugs for treating schizophrenia. In this thesis, the influence of surface modification of glassy carbon electrode with graphene in 0.1% Nafion solution on quetiapine voltammetric response was investigated. The purpose of this research was to define can the modification of electrode with graphene lead to development of a new electroanalytical method for the determination of quetiapine. Measurements on modified electrode have shown that the peak current observed at the potential of 1.06 V was higher and well-defined compared to the peak current obtained at unmodified electrode. Graphene enhances the peak current of examined medicine because it significantly increases electrode surface area and facilitates the electron transfer reaction. Nafion as polymer contributes to better binding of graphene on the electrode surface. Also, Nafion as cation-exchange polymer provides the adsorption of positively charged drug molecules on the electrode surface. Cyclic voltammograms of quetiapine in Britton-Robinson buffer solutions at various pH values were recorded. The results have shown that the oxidation peak potentials were shifted to the less positive values by increasing the pH, suggesting that the proton transfer is involved in the oxidation reaction of quetiapine. Also, the pH value of 4 was selected as optimal for further measurements. To obtain a much more sensitive voltammetric response for analytical studies, the variation of the peak current recorded at modified electrode was monitored while changing instrumental differential pulse voltammetric parameters.