Abstract: To screen marine bacteria which can tolerate a high concentration of cerium ion (Cs⁺) and its mechanism, we obtained a bacterium from the sediments of offshore area of Guangxi. The strain could survive in an environment of 700 mmol/dm³+ and is the bacterium that has been reported to tolerate the highest concentration of Cs⁺ . This bacterium was named Bacillus sp. Cs-700 after it had been identified by morphology, 16S rRNA sequence, and physiological and biochemical characteristics. In the medium supplemented with 700 mmol/dm³Bacillus sp. Cs-700 not only was able to tolerate high concentration of Cs⁺ but also had a good Cs⁺ removal ability, and had the potential to restore the environment contaminated by radioactive cesium. This study can be taken as reference for ecological restorations of environment contaminated by radioactive cesium.