Test samples were obtained by cutting two rings at 1,8 m and 5,0 m hight. Each ring was a source of bark and wood from the sapwood and heart-wood zones. Investigations of mineral substances (ash) and chemical elements (K, Ca, Mg, Mn, Fe, Na, Zn, Cu, S, P, N2, Cl2 and Pb, Cd) content was done in wood and bark of 120 years old oak trunk. Bark contains more mineral substances than sapwood and heartwood. Sapwood contains more potassium than heart- wood and bark, while bark contains more of the remaining determined elements than sapwood and heartwood.