This paper presents the results of torrefaction of selected biomass samples which are important from the point of view of their potential use in Poland. The sample thermal treatments were carried out at various temperatures, analyzing the process parameters’ effects on biomass drying and torrefaction. Furthermore, the effect of the process parameters on biomass composition, including the content of volatile matter, fixed carbon, the elements C and H, and high heating value, was also investigated. The study results demonstrated that under specified temperature conditions, a temperature rise is observed, thus confirming the occurrence of exothermic reactions. It was also determined that the most significant variations in sample weight, changes in the volatile content and the contents of the elements C and H, as well as changes in the calorific value of solid residues, occurred for cases when the process temperature was increased from 250°C to 300°C. The test results also indicated that proper selection of the temperature of sample thermal treatment makes it possible to produce solid carbonatious char containing as much as 80% C, and characterized by a high heating value of up to 30 MJ/kg. The results presented in this paper confirm that the parameters of thermally-treated biomass may be controlled by the temperature of the process of its thermal treatment.