To establish the coating conditions for 57Co, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a rhodium plate. The thermal diffusion of electroplated Co into a rhodium matrix was studied to apply a 57Co Mössbauer source. The procedure to form a Co deposited onto Rh foil was established using two different electroplating baths: the acid-based buffer (pH 3) containing boric acid, sodium chloride, and saccharin, and the alkaline-based buffer (pH 10) containing hydrazine hydrate and ammonium citrate. The influence of different annealing conditions was investigated. From the results, the best diffusion degree of electrodeposited Co onto the rhodium matrix was obtained in an annealing process performed at 1100°C for 3 h in vacuum over 10−5 hPa.