Master thesis deals with the damage survey of historical timber roof trusses of the eastern tower of Late-Romanesque St. Martin’s Cathedral in Spišská Kapitula. The aim of the thesis was, following the in-situ survey carried out on 11th November 2017, to take eleven samples for the purpose of microscopic examination and subsequently, to measure the moisture of elements used for samples. FAKOPP UltraSonic Timer was used to determine the extent of the wood damage. It is a non-destructive method using ultrasonic velocity measurement. Tescan-VEGA TS 5130, ultra-fast scanning system with compensation for static and dynamic image aberrations or scripting for user-defined applications was used to determine species composition and extent of the infestation of wooden items used for wooden construction of timber roof trusses of the eastern tower by wood- destroying fungi and insects. Outcomes of the survey are mentioned in the final part of the thesis. We found out that fir species (Abies alba Mill.) are originally used for major items, whereby three samples of the binding rafter were from larch species (Larix decidua Mill.). We proved the occurrence of fungi affecting cellulose and lignin degradation as well as wood destroying insects. According to typical damage inflicted by wood destroying insects, following species were determined: longhorn beetle (Hylotrupes bajulus L), conifer ambrosia beetle (Trypodendron lineatum L. ) and powder post beetle (Anobium punctatum De Geer). Following the outcomes, reconstruction and protection project as well as arrangements to maximise the tower lifecycle were proposed.