Fukushima Nuclear Power Plant was destroyed by the Great East Japan earthquake in 2011, and contamination by radioactive cesium widely spread to increase the concentration of cesium in sea sludge at Tokyo Bay by 1.5 to 13 times. The present study is thus to examine whether previous methodologies that demonstrated decontamination of sea sludge under anaerobic conditions might also be applicable to removal of radioactive cesium. Experiments employing a model mixture of cesium nitrate (CsNO3) showed that an anaerobic condition was unsuccessful for cesium decontamination from sea sludge. Microorganisms activation was seemingly realized, but expected decontaminating effects were not observed. Since a similar experiment with use of micro-bubbles has been successfully carried out, such an aerobic condition is to be improved to bring about an optimum performance. © (2014) Trans Tech Publications, Switzerland.