Several investigations have been directed towards the study of valence changes of substituted ions and accompanying variations of optical and EPR spectra. In this paper, the EPR spectra of Mn doped sapphire measured before and after neutron irradiation are reported. After neutron irradiation the results of EPR spectra show that the concentration of Mn 2+ and Mn 4+ decreased obviously. The changes of concentration of Mn ions have been also measured using optical experimental techniques and thermoluminescence experiments.