Ageing and degradation of natural and synthetic materials is a nature and irreversible process in which significantly participate societies of bacteria and micromycetes. From the viewpoint of biodeterioration of building and decorative materials, mainly the micromycetes are important and interesting. On architectural sights micromycetes are undesirable not only from the aesthetic point of view but also mainly for their degradation activity which accelerates gradual destruction of the building materials. The destructive activities of micromycetes were confirmed in the research of the late Gothic wall paintings in the chapels Stephaneum and Konvikt (18th century) in Trnava, of the tombstones places in the crypt of rabbi Sofer (17th century) in Bratislava and the interior walls of the monastery church in Okoličné (15th century).