We propose a method for the decontamination and waste volume reduction of cesium-contaminated soil. The soils were solidified with an interpolyelectrolyte complex solution and classified into several size fractions by wet sieving. Gamma-ray spectrometry of these fractions showed that the distribution ratio of the activity concentration of coarse soil particles decreased, whereas that of soil particles under 0.075 mm increased relative to reference samples. Results showed that the fine soil particles, on which radioactive cesium accumulates, were removed from the surface of the coarse soil particles during sieving and washing, and remained in the washing water.