Lost foam casting is a new method for casting complex parts. This method, in addition to its technical and economic advantages over the traditional methods, has environmental benefits and therefore has been of special interest. In this study, the effects of foam density, pouring temperature, and coating viscosity were studied, which are the most important factors affecting porosity and hardness in the lost foam casting method. The Taguchi method, signal to noise ratio and analysis of variance were used to design experiments and determine the optimal levels of each variable. All the considered variables were evaluated in three levels using L9 orthogonal array Taguchi analysis. Results showed that foam density of 20 kg/m3, pouring temperature of 740° C and coating viscosity of 20 sec were the optimal values for the variables due to creating appropriate condition between thermal decomposition and foam evaporation with speed of melting advancement and exhaust gas through the pores in the coating and creating lowest porosity (2.6%) and highest hardness value (27.7 HRA). Foam density and pouring temperature were the most influential parameters on the porosity and hardness with the impact factors of 64.58% and 56.35%, respectively.