In this paper, the starting materials necessary for producing magnesium oxychloride cement (MOC) were produced from dolomite ore using leaching-carbonation-evaporation-pyrohydrolysis processes. The influences of the molar ratio of MgO/MgCl2 (M-x) and H2O/MgCl2 (H-y) on the properties of the MOC (cured for 7 days) were determined using physico-mechanical methods. SEM and XRD analyses were conducted to determine the change of phase and microstructure of the selected 7-day MOC depending on the production conduction. The experimental results show that the best mix proportion of 7-day MOC was found to be M6.06H14 and its thermal conductivity, flexural strength, and compressive strength values were found to be 1.202 W/mK, 4.22 MPa, and 87.7 MPa, respectively. The water resistance of the MOC was improved by a small amount of H3PO4 (4% of MgO by weight). Consequently, if MOC is produced from dolomite, high-purity synthetic aragonite and CO2 would be obtained as byproducts, which are strongly demanded.