Abstract: The effect of heat treatment on the reactivity and microstructure of chars prepared from the vitrinites of two coals ( Yuxian lignite vitrinite (YXV) and Jianjiang bituminous coal vitrinite (JJV)) was investigated using X-ray diffraction(XRD) and Thermal Gravity Analysis(TGA). The results from TGA show that the reactivity of the chars from YXV and JJV decreases with the increase of heat treatment temperature. The reactivity of YXV char decreases quickly and significantly as the heat treatment time increases. However, after 60 min of heat treatment , it decreases slowly with time. The effect of heat treatment time on the reactivity of JJV char is slight. The results from XRD show that the microstructure of coal-char is determined by the intensity of heat treatment. When the heat treatment time is above 60 min, the structure of crystallites of YXV char prepared under 900℃ changes obviously and becomes more orderly. The aromatic layer stacking heights (Lc) of YXV char increase with the increase of heat treatment time when the heat treatment is conducted above 900℃. The effect of heat treatment time on Lc of JJV char is not significant, but under the heat treatment temperature of 1200℃, the crystalline of JJV char grows distinctly. There is a good parallel relationship between the crystalline growth and the deactivation of chars. It can be concluded that the growth of crystalline is the main reason for the deactivation of coal-char.