Cross laminated timber, or CLT, has been gaining popularity for its possible usage in the construction of multi-storey buildings. In our country, however, the construction of wood-based constructions, as opposed to the surrounding landscapes, lags behind. The reason is the legislation not adapted to the modern building trend and at the same time understanding the wood as flammable, for the construction inappropriate material. The diploma thesis deals with cross laminated timber constructions, their material, design and behavior under high temperature conditions in fires. The thesis process, evaluate and compare the results of testing the cross laminated timber and the frame-to-frame construction exposed to the heat source. For the equivalence of the tested samples, the samples are free of fire resistance enhancing features. From the measured results, we found that CLT is a suitable material for construction. Under model conditions of a fully developed indoor fire, the temperature on the unexposed side of the 3-ply CLT panel ranged between 18 - 20°C for 30 minutes. The layer on the exposed side served as natural protection in the form of a char layer which caused that middle layer peak temperature during this period was 110 °C. Thanks to the cross-arranged layers, the sample retained its strength properties. With the application of suitable protective materials, the use of cross laminated timber is more than adequate for the construction of multi-storey buildings.