The Effect of die surface modification on the physiochemical melt-out phenomenon was investigated. To measure the melt-out resistance more accurately, the mean depth measurement method after immersion in molten Al-alloy was proposed instead of the conventional weight change method. The validity of the mean depth method was verified by the comparison with the field service test of core-pin. The several kind of nitriding, such as gas nitriding, ion nitriding, salt-bath nitriding and TNHT process of PHILOS TECHNOLOGIES, INC were employed to change surface condition and their effects on melt out resistance were examined by the immersion test and the field service test of core pins. The melt-out depth was decreased with the nitriding treatments and in case of ion-nitrided specimen showed 2.8 times lower dissolution depth than as heat treated specimen. The white compound layer play a important role in the prevention of physiochemical reaction, therefore, the TNHT process, which does not form the white layer, was less effective in the view point of melt-out phenomenon only. The field test result using core-pins for producing automobile engine parts showed similar tendency with the mean depth method and this implies that the mean depth method reflects the melt-out resistance of the modified surfaces effectively.