Due to the accident at Fukushima Daiichi Nuclear Power Plant in 2011, the contamination of sewage sludge by radioactive cesium (Cs) took place. Sewage sludge containing radioactive Cs will be processed according to the Act on Special Measure concerning the Handling of Pollution Radioactive Materials, but behavior of radioactive Cs in sewage sludge is not clear. In order to reveal existence form of radioactive Cs in sewage sludge, we investigated the distribution of radioactive Cs in sedimentary sand, dried sludge, melted slag and fly ash by the IP, SEM-EDS and TEM/STEM. As a result, it was shown that radioactive Cs in sedimentary sand and dried sludge are adsorbed on several particles of weathered biotite mainly, and radioactive Cs in melted slag and fly ash are uniformly distributed.