The investigations were carried out on 1-3- and 10-year-old stems and on the trunks of beech. The optical properties measured were: reflectance, absorption and transmittance of irradiation. The reflectance was measured in the bark and the cork, while absorption and transmittance were measured on isolated cork. Reflectance was measured only on the bark of trunks and the range of the investigations was 400-1100 nm. The reflectance of irradiation in the stems increased with increasing wavelength and decreased with the age of stems. In the range 400-700 nm it ranged from 18% in 1-year-old stems to 10% in 10-year-old stems, and reflectance in the trunks was equal to 15%. In the range 700-1100 nm, it ranged from 51% in 1-year-old stems to 36% in 10-year-old stems and in the trunks. Absorption of the cork decreased with increasing wavelength from about 92% in the range 400 nm to about 15% in the range 700 nm, and to 15% in the range 1100 nm. Any distinct influence of stems age on cork absorption was not observed. Transmittance of irradiation increased with increasing wavelength and the age of the stems. In the range 400 nm it was >1% in all age groups of the stems. In the range 700 nm in 1- and 2-year-old stems, it was equal to approximately 45%, and in the 10-year-old ones it amounted to 60%. In the range 700-750 nm, transmittance decreased to about 38% in the bark of 1-3-year-old stems, to 50% in 10-year-old ones and it remained at this level up to 1100 nm.