The surface of boron-doped diamond (BDD) electrodes has been modified by Nafion®. The polymer film was applied onto the BDD electrode surface by solvent evaporation. Nafion®-BDD electrode was used as a sensor for caffeine detection in e.g. cola beverage samples. In cyclic voltammetric measurements, favorable ionic interaction between the Nafion® film and caffeine enhances the current response, and thus the sensitivity, compared to that at the bare electrode. The modified electrode exhibits a stable and sensitive response to caffeine and may represent a new analytical tool, offering a significant improvement over other electroanalytical methods (e.g.: Nafion®-modified glassy carbon electrode) and the accepted method for caffeine analysis (HPLC-MS). The analysis of residuals from the linear regression proved that a linear response exists from 2.0 × 10− 7 to 1.2 × 10− 5 M, obtaining a limit of detection of about 1.0 × 10− 7 M. The findings presented in this study are described and discussed in the light of the existing literature.