This paper reports a novel approach to enhance the rate of heat extraction from sand castings by flowing helium gas through the sand mold during the course of the process. The effect of helium flow rate, flow direction, and mold design on the thermal profile, grain size, secondary dendrite arm spacing, and tensile properties of the castings is investigated. An optimum set of process parameters is identified and a “performance index” for assessing the efficiency of the helium-assisted sand casting process is defined. It is found that when the helium-assisted aluminum sand casting process is performed with close to the optimum parameters, it produces castings that exhibit a 22 percent increase in ultimate tensile strength and a 34 percent increase in yield strength with no significant loss of ductility and no degradation in the quality of the as-cast surfaces.