The aim of this study was to determine the thermal characteristics and structural changes of pelletized biomass at different moisture contents. Miscanthus, Jerusalem artichoke and Spartina pectinata at 10, 20 and 30% moisture contents were used. Irrespective of the type of biomass, heating induced changes in the FTIR bands at 875 and 1420 cm(-1), characteristic of lignin monomers and amorphous cellulose, respectively. An increase in the crystallinity index was observed, and the most resistant to compressive loads pellets were obtained with a 20% moisture content of Spartina and Jerusalem artichoke. Miscanthus and Jerusalem artichoke had the same trends in the distribution of their maximum cellulose melting points temperature peaks according to the moisture content used. For Miscanthus, this temperature was higher by 24 degrees C than for Jerusalem artichoke, and two-step decomposition of cellulose was observed, while one-step decomposition was observed for Jerusalem artichoke as well as for Spartina. The novelty of these studies was the use of modern instrumental methods (DSC and FTIR) to better understanding the changes occurring in biomass with a wide range of moisture content (10-30%) as a result of heating the material during the pelleting process.