<p>This study evaluates the use of marble waste as a substitute for conventional silica sand in green sand molding for foundry applications. Marble waste, composed primarily of calcium carbonate (CaCO₃) with minor amounts of Al₂O₃, SiO₂, and Fe₂O₃, was assessed for its compatibility with standard molding practices. A central composite design within response surface methodology (RSM) was employed to optimize mold composition, varying bentonite clay content between 8 and 12 wt% and moisture content between 2 and 7 wt%. The model identified an optimal formulation of 12 wt% bentonite and 3 wt% moisture, yielding molds with desirable mechanical and physical properties. Experimental validation showed that the optimized marble waste mold achieved a hardness of 92, permeability number of 270, compressive strength of 1.39 kg/cm² (0.128 MPa), and shear strength of 0.39 kg/cm² (0.038 MPa). Comparative trials using A356 aluminum alloy castings revealed that marble waste molds produced castings with comparable hardness, surface finish, and microstructure to those made with traditional silica sand. These results demonstrate the technical viability of marble waste as an alternative molding material. Further investigation into its recyclability and long-term performance is recommended to support broader adoption in foundry operations.</p>