Ancient copper coins from the Greek cities Nicopolis in Epirus and Thessaloniki in Macedonia, minted during Roman Imperial times (31 BC-268 AD), have been analyzed nondestructively by particle-induced x-ray emission (PIXE). The coins covered practically the whole production period of each mint. There were 11 elements detected and determined quantitatively, five major and six minor ones. The coins were analyzed before and after removal of the patina. From the results obtained so far, significant variations were observed in the composition of the coins from emperor to emperor and from city to city. This is the first part of a study, the final aim of which is to examine the economic life of these two cities under the Roman occupation, covering the period from Augustus to Gallienus.