Coal fly ash was examined for the removal performance of trichloroethylene (TCE) from gas phase. The performance of coal fly ash was evaluated by gas chromatography in batch test and by FTIR spectroscopy in flow test compared to that of a clay mineral, allophane, and an activated carbon. The adsorption ability of the coal fly ash for TCE was significantly lower than that of the allophane and activated carbon due to its lower specific surface area. On the other hand, the TCE adsorption amount of the coal fly ash per its specific surface area was larger than that of the allophane and activated carbon. The coal fly ash is presumed to readily adsorb the TCE molecules because the Lewis acid sites on the calcium atoms in the coal fly ash strongly interact with the π electrons of the TCE double bond. The coal fly ash can be an excellent adsorbent when it consists of fine particles having a great amount of the Lewis acid sites on their surface.