The effect of coprecipitated MgO-Al2O3, MgO-Cr2O3and MgO-Fe2O3gel on the strength retainment properties of magnesium oxysulphate cement based basic castables has been investigated. Incorporation of MgO-Al2O3gel is found to be most beneficial for the improvement and retainiment of both the room temperature and high temperature strengths. SEM studies have been conducted to get an idea about the microstructure of castables cured at room temperature and heated at high temperature.