High temperature thermal behaviors of EAF dust by coke and char at initial reaction stage were studied to obtain the fundamental data of EAF dust treatment process. Coke and char were used to reduce zinc and metal oxides in EAF dust. In this study devolatilization of mixture(EAF dust : carbon materials : limestone = 80 : 10 :10wt%) were investigated as functions of reaction temperature(900-1150℃) and reaction time(3-12min.) and weight loss by TGA (heating rate : 5℃/min, 30ml-N₂/min.). Reactivity of coal char was more reactive than that of coke during short reaction times of initial reaction stage, but reduction degrees of coal char and coke were nearly close in case of long reaction times in EAF dust treatment process.