Сhanges of the Scots pine wood (Pínus sylvéstris) within a single tree trunk caused by its biological destruction made by red belt fungus Fomitopsis pinicola (Schw. ex Fr.) Karst were studied by use of the IR Fourier spectroscopy method. The wood was cut in Syktyvdin region of the Komi Republic. From the trunk about 36 сm in diameter a sample was sawed about 15 cm thick. Three samples were selected for spectra: 1 – light brown non-destructed wood from the centre of the trunk, 2 – dark brown, adjacent to the completely destroyed wood; 3 – from the periphery of the trunk not clearly affected by rot. The research was made by use of spectrometer Prestige-21 produced by Shimadzu company in the field of the wave numbers 4000–400 сm–1 with a resolution of 4 cm–1 (20 scans). Absorption spectra were examined by using a diffusion reflector (DR). It is shown that bio destruction of the wood fiber of pine is reflected on the IR Fourier spectra. Changes are observed in the absorption spectrum that characterize the valence oscillations of hydroxyl, methylene, carbonyl groups, and skeletal oscillations of the aromatic ring. A deep destruction of wood in the centre of the trunk is accompanied by a bathwater drift (1734 сm–1 to 1719 сm–1) and a significant increase in the absorption band of the valence oscillations of carbonyl groups (1719 сm–1), as well as change of the spectra contour of the absorption from ~1719 to ~1100 cm–1. In the spectrum of the disrupted wood, the intensity of the absorption bands in this area decreases, and in the spectra of the samples from the periphery and the center of the trunk that have preserved the morphological structure of the wood increases. There is a significant increase in the absorption band in the disrupted wood 1601 сm–1, that becomes bigger than, band intensity maximum 1508 сm–1, that is not typical for the IR spectrum of healthy coniferous wood, in which the ratio of the intensity of these absorption bands is the opposite.