Method for purifying water contaminated with radioactive cesium

The purpose of the present invention is to provide a method for purifying contaminated water containing radioactive cesium that makes it possible to selectively remove cesium from contaminated water that contains potassium, sodium, or the like and that can be safely performed without imposing a large burden on the natural environment. The method for purifying water containing radioactive cesium according to the present invention is characterized by comprising a step in which a salt of surfactin is added to contaminated water and caused to bond with radioactive cesium in order to obtain a cesium salt of surfactin.