This paper present the results of examination of wood of four black locust clones (Robinia pseudoacacia L.) R34, R56, R113, R121, in different ages – 6, 8, 11 and 13 years. Growth ring width, fiber length and wood volume density (oven dry and basic) were determined. For all tested roperties significant differences were found caused by different clone and different age of wood. The highest average growth rate – the width of growth rings was recorded up to the eighth year (mean 5.40mm), while the average fiber length of 0.866 mm increased with age of trees. Mean values of wood density of 672 kg/m³, which is in an older wood range up to 780 kg/m³ , confirm a significant possibilty of using black locust wood as renewable energy source.