In the cast iron industry, mould sand quality and the most efficient recovery of used sand into the system are critical. For this purpose, the optimum values of the factors (humidity, active bentonite and coal dust) affecting the green strength, gas permeability and shear strength of the mould sand were determined in this study. The optimum mixture ratio, which makes the green strength, gas permeability and shear strength of the mould sand the best, was made by using the mixture design method. As a result of the studies, optimum casting sand composition; the percentage of moisture content, the percentage of coal dust, the percentage of active bentonite and the percentage of recycle sand were determined as 3.92%, 0.05%, 0.30% and 95.73%, respectively. The green compression strength(B-1) 23.5 N/cm(2), shear strength(B-2) 7.7 N/cm(2) and gas permeability (B-3) 91 mmWS of the conventional cast sand prepared in this optimum composition were measured.