Abstract: A detailed procedure for the preparation of Mossbauer sources, having narrow unsplit emission lines, is described.The 57Co used in this work is obtained by irradiating iron in the cyclotron (1.5m) according to the nuclear reaction 56Fe (d, n)57Co. Cobalt is separated from the irradiated iron targets chemically and the plating solution is preparaed from the resulting 57Co. An appropriate source matrix is chosen. 57Co is deposited electrolytically on the cathode (source matrix), and diffused into the matrix by thermal treatment. The linewidths of sources thus prepared are 0.104-0.114 mm/s.