A parametric study has been conducted to investigate the influences of the molar ratios of MgO/MgCl and HO/MgCl on the properties of magnesium oxychloride (MOC) cement. By an integrated assessment of the experimental studies of strength development and X-ray diffractograms, together with application of the relevant phase diagram, it is recognized that the molar ratios of MgO/MgCl and HO/MgCl can significantly affect the properties of MOC cement. For a MOC cement paste possessing a dominance of 5MgO·MgCl·8HO (phase 5) crystals, the molar ratios of MgO/MgCl of 11-17 and HO/MgCl of 12-18 are found to be the most favorite ranges for design purpose. The choose of the molar ratio of HO/MgCl is, however, largely depends on the molar ratio of MgO/MgCl mainly for controlling workability of paste. Therefore, the most critical parameter to be selected in the design process is the molar ratio of MgO/MgCl, although the reactivity of the MgO powder is also important. Besides, the molar ratio can also be affected by the reactivity of the MgO powder to be employed. It is believed that a molar ratio of MgO/MgCl of 13, the most suitable one shown in this study, can be used as a starting point in the normal practice. © 2007 Elsevier Ltd. All rights reserved.