The effect has been examined of TiO2 on B2O3 content in sintered magnesium oxide samples obtained by precipitation of magnesium hydroxide in seawater with 80 or 120% of the stoichiometrical quantity of the precipitation agent, i.e. the effect of TiO2 on product properties has been examined. Coefficients were calculated for dependent reactions of Ca2B2O5 and CaTiO3 formation.