Wood is a material which, due to its organic origin, is subject to various degrading factors, and one of them is fire. If this material is to be used in the construction of buildings, it is subject to fire safety. In this respect, its fire protection plays an important role.At present, different protective devices are used for this purpose, with different properties and different effects. The bachelor thesis informs about possible ways of wood protection against fire and also describes the properties of substances with fire retardant effect, used for this purpose. Its main part is a comparison of the effectiveness of selected retardants and the effect they have on the change in weight of spruce wood impregnated by them under heat load.We have selected the following types of retardants: (Flamgard, Plamostop D Transparent, Plamor ok v 2026, Hr – prof, Drevostop (vodné sklo), Isonem Anti-Fire Paint), and data for comparison were drawn from available works of various authors.The evaluation showed that each of the compared substances contributed to the slowing down of the thermal degradation of spruce wood, although it should be noted that with a different effect. The best results were recorded by the retardant Plamostop D Transparent (decrease in weight loss compared to unprotected samples was up to 75%), on the other hand, it performed most weakly,, Drevostop (vodné sklo) the weight loss of protected samples over unprotected samples was only 5%.