Introduction: Generic drugs should have the same active ingredient than their reference drugs, at the same concentration, dose and dosage form. As the costs of generics are lower, many people have raised questions about their composition, efficiency and response time. A Scanning Electron Microscope (SEM) produces high magnification and resolution images through the interaction of electrons with the sample atoms. This equipment may also be used to perform a multielement analysis using an Energy Dispersive Spectroscopy (EDS) system. Objective: Given the SEM/EDS features and the questions raised on the use of generics, we carried out a qualitative analysis of the reference, generic and similar drugs of Potassium Diclofenac (50 mg), in order to verify their compositions and compare them. Materials and Methods: Three different brands of each drug (reference, generic and similar) were tested. The samples were irradiated for 300 seconds using a SEM/EDS Hitachi TM-3000 microscope, with three measurements at different points in each tablet. The measurements were also made with the drug without the coating. Results: The technique was able to detect the constituents present in both the excipients and the active ingredient of the drug. Some differences were found when the samples were irradiated with their coating. On the other hand, all generic drugs were found to be qualitatively similar to their reference drugs when the coating was removed. Conclusions: The technique was proven efficient and suitable for the samples, because through the spectra of the generic and similar drugs it was possible to identify not only the active principle but also the excipients, and compare them to the reference drug. DESCRIPTORS Drug. Generic. Diclofenac Potassium. Spectroscopy.