In this research, the calorific value and ash content of wood and bark of some fast-growing hardwood species, such as tree-of-heaven, (Ailanthus altissima (Miller) Swingle), empress tree (Paulownia tomentosa (Thunberg) Steudel), trembling aspen (Populus tremuloides Michaux), oriental plane (Platanus orientalis Linnaeus) and black locust (Robinia pseudoacacia Linnaeus) were investigated in order to comprehend their behaviour during combustion and estimate their utilization potential as solid biofuels (pellets). Beech (Fagus sylvatica Linnaeus) wood was used for comparative reasons. Different ratios of all the studied species in mixture were examined in order to investigate the material ratio that provides a satisfactory calorific value, while parallelly meeting the ash content requirements of the pellet production standard (ISO 17225-2:2014). Black locust bark seems to greatly increase the calorific value of the material. Empress tree wood had the lowest ash content, meeting the requirements of the best class (ENplus A1 – residential use), while tree-of-heaven and poplar were classified into ENplus B class (third class of residential use). By using the appropriate proportions, all the materials examined could be utilized in pellet production.