AbstractThis work analyses the anti-fungal efficacy and stability of 10 essential oils, as well as their colour stability, in wood. The efficacy of oils against the decay fungi Coniophora puteana and Trametes versicolor as well as the moulds Aspergillus niger and Penicillium brevicompactum was evaluated first on filter papers treated with 1, 3.5, 10%, or 100% concentrate, and then on beech wood treated with 10% solutions. Accelerated ageing of treated beech samples was done before mycological tests and consisted of heating, leaching followed by heating, and Xenotest followed by heating. The highest growth inhibition of moulds and C. puteana was caused by thyme, oregano, sweet flag, and clove oils, while the savory and birch oils were less effective. These oils are potentially useful for wood protection against brown-rot fungi and moulds, mostly in interior conditions. The essential oils had only a negligible effect against the white-rot fungus T. versicolor, which was more apparent after previous ageing of wood. Some essential oils with a yellow tone (birch, oregano, sweet flag, savory, and tea tree oils) significantly changed (p<0.05) the natural colour of beech wood, but the new colours were relatively stable and underwent only mild changes after accelerated ageing in Xenotest.