It is known that oxidation rate of coal is roughly related to coal rank. Recently, the amount of low rank coal （semi soft caking coal） which we utilize is increasing in coking process. It is important to develop how to stock coal safely in indoor hopper for steel industries. In this paper, to investigate the influence of the sample mass and atmosphere temperature for the evaluation of self-heating characteristics for coals, three experiments （used sample mass at each of experiments was a few grams, a few kilograms and a few hundred of kilograms） were performed. These two results were obtained. 1） The effect of sample mass is very sensitive to the rate of self-heating. 2） The adiabatic apparatus for evaluation system of self-heating characteristics on coal is needed.
