This paper deals with research concerning the graphene-doped construction materials, namely with the optimization of the ideal content of the nanoadditive in the final composite. This research was conducted building on the previous studies on use of graphene in magnesium oxychloride cement (MOC). The evaluation of the effect of the graphene nanoplatelets based on their content was performed using various analytical methods as well as mechanical tests. Among the used methods are XRF, SEM, EDS, HR-TEM, XRD and OM. After 28 days of air curing, the mechanical, macro- and micro-structural parameters were studied. One of the main characteristics of the materials was their porosity, which was thoroughly studied in order to determine the influence of the graphene on its drop. This parameter is very important for the MOC-based materials, hence it is directly connected to their resistance to water. The compressive strength of the sample containing 1 wt% of graphene reached value of 99.7 MPa. This sample has shown a massive increase in both compressive (26.8 %) and flexural strength (14.9 %) as well as in the modulus of elasticity (73.1 %) in comparison with the reference sample which did not contain any additives. The developed composite materials show a promising route in the controlled improvement of reactive magnesia-based construction materials properties using carbon-based nanoadditives.