The effect of carbon equivalent on the fading behavior of hypoeutectic ductile cast iron was investigated. The carbon content was slightly increased right after graphite spheroidization treatment and remained almost constant with holding at $1,490^{circ}C$ after 4 minute. The residual magnesium content was decreased slowly with holding. The empirical equation expressing the relationship between this and holding time was proposed ; $C=C_o-P{ imes}t$. The proportionality constant, P, was inversely proportional to carbon content.