An experimental study of the conversion of Japanese municipal solid waste (MSW) to solid fuel by using an innovative hydrothermal treatment has been performed. The treatment system is capable of processing up to 1 ton MSW per batch, applies medium-pressure saturated steam at the pressure of approximately 2 MPa in a stirred reactor for one hour. After undergoing the process, MSWs of various sizes and forms became slump materials that were easily dryable to a powdery product with a 10% moisture content and an average heating value of 20 MJ/kg (dry basis), which is equal to that of low-grade sub-bituminous coal. Because the MSW used in the experiments contained a significant amount of plastics, the reduction of chlorine content, which is known to promote clogging, corrosion, and dioxin formation in the furnace, was imperative. It was observed that water-insoluble organic chlorine generated from poly vinyl chloride containers was approximately 10,000 ppm (dry basis) in the raw MSW and was reduced to approximately 2000 ppm (dry basis) because of the transformation to water-soluble inorganic chlorine during the hydrothermal process. These changes in chlorine content were very evident at elevated temperature and pressure. These results indicate that the hydrothermal treatment is a viable way to treat MSW and obtain an alternative low chlorine content solid fuel. (C) 2011 Elsevier Ltd. All rights reserved.