The aim of the paper is to present a relatively new technology – hydrothermal carbonization (HTC) of municipal sewage sludge. The HTC process was conducted in a stainless steel, Zipperclave Stirred Reactor, with a volume of 1000 ml, equipped with a MagneDrive Agitator. The control panel provides a programme which regulates the heater temperature and mixer speed. The main parameters of the process were temperature (~200°C), pressure (~1.5 MPa) and residence time (4, 7, 10, and 12 h). In order to understand the process, the physical, chemical, thermal, and structural characteristics of the solid product, hydrochar, was investigated. Therefore, the ultimate and proximate analyses, and HHV for raw material and obtained hydrochar are presented. The majority of carbon, of the initial present carbon, remained within hydrochar. TA analysis was used to detect the initial and final temperature for the combustion of raw material and hydrochar. This technique is very useful for predicting the combustion characteristics of carbonaceous material. When considering the use of hydrochar as a solid fuel, more energy can be derived from hydrochar than from e.g. incineration of waste, and its carbon emission should be less significant. Therefore, HTC can be an environmentally beneficial technique for the combustion process.