In this paper, we presented an investigation of the theoretical and the industrial definitions of the metallic calcium production by metallothermic process in the vacuum atmosphere. In the studies, Al is the only reductant that is used for the metallothermic calcium production. In experiments, effects of percentage of Al stoichiometry as a reductant, time variances of reduction and temperature of reduction were investigated. In this study, experiments were carried out at 1200, 1250, 1300 degrees C and 100% Al, 125% Al and 150% Al stoichiometry to produce metallic calcium from the residue of metallic magnesium production residue. All raw materials and residue phases were characterized by using atomic absorption spectrometry (AAS), X-Ray Diffraction Spectrometry (XRD) and chemical analysis techniques. From the results of these experiments, it was understood that the use of Al with the increasing stoichiometry increases the efficiency of the metallic calcium production with the increase of reduction time.