Scanning electron microscopy (SEM) with energy-dispersive microanalysis (EDS) and energy-dispersive x-ray spectrometry (EDXRS) were used to investigate the composition and microstructure of some Roman coins from the Julius Caesar and Octavianus periods. The samples were Cu-based alloys with different surface conditions. The microstructural examination supported the chemical analysis data, explaining compositional changes from the surface to the bulk. Compositional data confirm the numismatic interpretation: coins issued by Julius Caesar were orichalcum (Cu-Zn alloy) coins whereas asses issued by Octavianus were Cu-Pb-Sn coins.