Incineration is the most common method of treating municipal waste. By this method, harmful organics are converted to harmless gases. However, the elution of harmful trace elements from the incineration ash is a cause for environmental concern. The present study examined the elution and leaching characteristics of fly ash packed in a column on elution with nitric acidic solution. At a certain stage in some experimental runs, the pH of the acid leachate decreased sharply, the flow rate of the leaching solution increased, and the concentrations of the main or major inorganic elements Al, Zn and Fe increased sharply. These phenomena were explained as follows. At the first stage of experimental runs, the major element Ca was dissolved, and the pH of the eluate increased with pH gradient in the column. The main or minor elements Al, Zn and Fe dissolved in the upper part of the column were precipitated at bottom of the column, leading to reduction of the flow rate of the leaching solution. With the complete dissolution of Ca, the eluate pH decreased, these deposits were dissolved and the flow rate increased. It was found that the leaching experiments depended strongly on packing conditions such as initial wetting of fly ash, the presence of cracks, packing density and packing height. The present study on leaching characteristics of fly ash suggested that a drastic increase in harmful trace elements might occur even after the pseudo-stable dissolution from a land-fill site.