Cadmium contamination of soil is one of the most serious environmental problems in Japan. As basic research toward the development of a decontamination method to remove cadmium from soil, cadmium transport has been measured in a volcanic ash soil during citric acid solution flow. After a soil column that was polluted artificially by cadmium nitrate was saturated with distilled water, citrate solution was passed through the soil column. Leachate from the soil column was collected for the measurement of cadmium concentration. At the end of the flow experiment, the soil column was sliced into 2-cm-thick pieces and the residual cadmium in soil was analyzed. As a result, it was found that the higher the concentration of citrate, the faster the cadmium discharged from the soil. This result can be explained in terms of the downward movement of the soluble complex of citrate with cadmium in the soil.