The durability of fire protection impregnation is of great importance in the case of protection of wooden structures. At the same time, impregnation itself can affect the physical properties of wood, worsening its characteristics. As part of the project POIR.01.01.01-00-0076/21, research was conducted to check how the hygroscopicity of scots pine wood obtained from wood graded for strength to KS class changes depending on the impregnation agent used in the surface and deep impregnation methods. As a result of the research, it turned out that wood modified with salt-based fire protection agents is less sensitive to changes in ambient humidity than raw wood.