Mold filling characteristics in the Mg Expendable Pattern Casting(EPC) process were investigated in terms of casting conditions such as reduced pressure, pouring temperature and casting modulus including foam materials. With increasing pouring temperature up to 775 degrees C the filling velocity increased. However, the filling velocity decreased at temperatures above 775 degrees C. This is likely due to the increase of back pressure. Concerning the effect of reduced pressure on filling velocity, it increased sharply at lower reduced pressure while became stable at higher reduced pressure. In thick pattern, high reduced pressure would be needed to obtain high filling velocity. In expanded polystyrene(EPS) patterns, mold filling was found to be faster in the thick pattern than thin pattern at temperatures below 750 degrees C. This propensity was observed to be reverse at pouring temperatures above 750 degrees C. In polymethyl methacrylate(PMMA) patterns, the filling velocity almost leveled off without showing a dependence of pouring temperature. This result is attributed to the difference in gas pressure between EPS and PMMA patterns during the EPC process.