The mold filling for a thin wall aluminum alloy casting in the expendable pattern casting process was investigated experimentally and theoretically. Thin wall aluminum alloy plates were cast by the EPC process. The fluidity length and melt velocity were measured. The use of thin expendable polystyrene pattern led to shorter fluidity length of melt. When the coat permeability was less than approximately 2, the fluidity length of the melt and melt velocity increased with increasing of the coat permeability. When the coat permeability was greater than approximately 2, even when the coat permeability increased, the fluidity length of the melt and melt velocity did not increase so much. The fluidity lengths were predicted by using measurement values of the melt velocity. The predicted values were in approximately agreement with experimental values.