Abstract: Abstract: Biologic agar-block method was developed that allowed wood samples to be evaluated and monitored in terms of colonization and development of the decay by Basidiomycetes fungi (Coriolus versicolor) and to be directly classified based on mean mass loss. In this research, the in vitro decay of five commercial woods by Coriolus versicolor was studied by the agar-block method. The selected wood samples were Abies alba, Populus alba, Fagus orientalis, Platanus orientalis and Ulmus glabra. The results demonstrated the strong resistance of Ulmus glabra and the lowest resistance in Fagus orientalis. The mass losses (%) were 16.8 and 42.4%, respectively. There were also a high correlation between the mass loss and apparent damage. Therefore biological evaluation of wood regarding biodegradation and the selection of wood types for various application respects will be of high priority.