Thermal expansion and hot deformation are two phenomena that cause dimensional errors in investment casting. This error occur in dimensions between the die pattern and the wax pattern. Therefore, the wax's thermo-physical and thermo-mechanical properties, the metal die features, and the process parameters affect the dimensions of the wax pattern. Some important effective process parameters are the injection temperature, the injection temperature, the die temperature and the holding time. In this paper, the effect of injection parameters on dimensional accuracy of wax models created by a metallic die has been studied. The Taguchi formulation based on design of experiments has been applied in order to obtain the optimum condition to achieve the best dimensional accuracy. The studied specimen with “F” shape has 10 dimensions. The root mean square (RMS) of dimensional differences has been considered for accuracy analysis. The results has shown that if the injection temperature, the injection pressure and the holding time be considered as 80oC, 20 bar, and 2.5 minute, respectively, the best accuracy may be achieved.