The results of bark thickness analysis of pine and spruce trees at the thinning age are presented in the work. The main goal of the work was to investigate regularities of bark thickness variance of pine and spruce logs produced out of trees felled during the thinning cuttings. The main tasks of the work were to find out regularities of bark thickness variance depending on age of the stands, tree species and top diameter of the log, to evaluate adequateness modeled regularities to existing Swedish normatives. The empirical material. 200 pine and 200 spruce felled trees at the Kazlu Ruda state forest enterprise were used for the measurements. The trees were selected at the 4 cutting areas of Nb, Lb, Lc, site types. Diameter and bark thickness of imaginative crosscut at height of 0, 1, 1.3, 3 m and following each second meter were measured for each stem. Methods. The multiple linear and nonlinear regression were used to process empirical data. Calculations were made using software STATISTICA v6.0 and EXCEL. The main results. The differences of bark thickness variation regularities were found while comparing gotten results to Existing Lithuanian and Swedish legalized normatives.