We found that bacteria in a commercial soil conditioner sold in Ishinomaki, Miyagi, exhibited concentrative and saturable cesium ion (Cs⁺) uptake in the natural range of pH and temperature. The concentration of intracellular Cs⁺ could be condensed at least a few times higher compared with the outside medium of the cells. This uptake appeared to be mediated by a K⁺ transport system, since Cs⁺ uptake was dose-dependently inhibited by potassium ion (K⁺). Eadie-Hofstee plot analysis indicated that the Cs⁺ uptake involved a single saturable process. The maximum uptake amount ( J _max) was the same in the presence and absence of K⁺, suggesting that Cs⁺ and K⁺ uptakes were competitive with respect to each other. These bacteria might be useful for bioremediation of cesium-contaminated soil.