Poplars and willows are widely used to produce biomass for energy. Calorific values of wood and bark, as well as for whole tree of Populus x euramericana (cl. I-214), Populus deltoides (cl.PE 19/66) and white willow Salix alba (cl.378) of different ages were determined. one- and 2-year-old rooted cuttings were grown in plantations with high planting density, in order to produce a high biomass yield per hectare. Mature trees in both species (poplar and willow) originated from the corresponding plantations; willow 14-year old, and poplar 12 years (cl.1-214) and 8 years (cl.PE 19/66). As the share of bark depends on the age of wood, calorific values were determined separately for bark and for wood. The share of bark (proportion of total weight) in 1- and 2-year-old rooted cuttings ranged between 18% and 27%, and in older trees it was from 10% to 15%. The higher heating values of oven dry poplar wood (calculated for the whole tree, based on the proportion of bark) were from 15,787 (cl.1-214 1-year old) to 24,275 kJ/kg (cl.1-214 2-year old). The average calorific values of willow wood (whole tree with bark) were from 16,169 (14-year old) to 22, 572 kJ/kg (2-year old). It should be pointed out that the calorific value of wood is more favorable than that of bark, and the highest calorific values refer to 2-year-old trees.