The thermoplastic behavior of coal under various heating conditions was investigated using the rapid heating plastometer that was developed in this study. Coal samples were heated at a rate of 3-1800K/min with this instrument and the torque applied to the stirrer, which rotated at a constant speed, was measured. This torque was converted to apparent viscosity of coal in a plastic state. As the thermoplastic behavior of coal, minimum apparent viscosity and all the characteristic temperatures corresponding to softening, maximum fluidity and resolidification state observed by Gieseler method was estimated. Coal thermoplasticity was strongly dependent on the heating rate under the condition of rapid heating. All the characteristic temperatures were shifted to higher values remarkably while the minimum apparent viscosity decreased with the increase of heating rate. The minimum apparent viscosity decreased in case of weathered coal, which never shows Gieseler plasticity, over the heating rate of 1000K/min. The addi-tivity of the minimum apparent viscosity was also examined for blended coals. Though no additivity was observed at low heating rate, with the increase of heating rate the difference between additive value and observed value became small.
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