Abstract.This paper reports the effect of aluminium corrosion reaction on the density, porosity, and thermal insulation capability of porous fire bricks. The reaction between aluminium and alkaline solution produces hydrogen and other sediment products. The test specimens of fire bricks were made from the mixture of castable cement, aluminium powder of 325 mesh in size (0, 0.1, 1, and 2 wt% with respect to castable cement), and 0.185 M KOH solution. The structural examination of the specimens shows the increase of porosity to 22.7 -30.6% and the decrease of density in the range of 1.135-1.503 g/mL. In addition, the samples possess average pore size of 0.001-0.003 cm 3 with the thermal insulation in the range of 47-78%.