In this present investigation, approaches were made to examinethe effect of mineral charac teristics on ash deposition using a laminar DTF (Drop Tube Furnace) with variation of operat ing condition such as different coal size, deposited surface temperature and flue gas tempera ture. To simulate the ash deposition environment inside of the gasifier, cylinderical DTF(Drop Tube Furnace) was used in the experiments. Five different samples of pulverized coal , such as Datong coal, Xinhua coal, Zhongmei coal, Kideco coal and Roto coal were examined inthe DTF under various conditions such as deposi t surface temperature, flue gas temperature and gas environments. The ash particles are dep osited onto sample collector by impacting and agglomerating action. The deposit ashes werec ollected, weighted, and analyzed to determine the amount and composition of deposit. Finally, developed fouling index of ash deposition at low temperature will be refined with the ash deposition behavior in DTF.