The aim of this work is to develop a novel method for the immobilization of radioactive cesium (Cs) compound, and this can be applied to the treatment of real biomass items contaminated with Cs which had spread over a wide area from the Fukushima Daiichi Nuclear Power Station in March 2011 in Japan. In the same group of alkali metal Cs, potassium (K) was first used for optimizing experimental conditions. The chemical composition of Cs in the contaminated biomass is believed to be similar to Cs2CO3, so that K2CO3 was used as a model starting sample added to cellulose, called as CK mixture, and further with kaolinite, as CKK mixture. Both CK and CKK mixtures were separately ground by a planetary ball mill, and the ground products were heated at different temperatures in air. Heating both mixtures at 600 degrees C enables us to reduce their weights effectively, due to mainly decomposition of cellulose. Finally, the mixture containing cellulose, kaolinite and Cs2CO3, as CKC mixture was investigated under the optimized conditions. As a result, the formation of water-insoluble Cs compound in the calcined sample with kaolinite addition after milling operation was achieved. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.