PURPOSE: The green sand mold molding sand which is increased of compressive strength by adding any of magnesium oxide, magnesium hydroxide or magnesium carbonate together with bentonite and water to aggregate.

CONSTITUTION: Magnesium oxide; 0.5W20wt% based on the weight of bentonite, or magnesium hydroxide; 0.7W30% or magnesium carbonate; 1.0W40% is added together with bentonite and water to aggregate such as silica sand, zironium sand, chromite sand, olivine sand, carbon sand or aluminum sand, and the mixture is kneaded. This composition increases the compressive strength of the green sand mold molding sand the enables the coping with the higher speed and higher pressure of casting.