In a method for improving the acoustic properties of spruce resonance wood for musical instruments at least one resonance wood blank is subjected to a treatment with Physisporinus vitreus under controlled, sterile conditions. The previously sterilized resonance wood blank is immersed into a liquid medium enriched with fungus myecelium and kept therein in the dark for an exposure time and finally sterilized, wherein during the exposure time a temperature of 18 to 26° C. and a relative humidity of approximately 60 to approximately 80% are maintained. Due to the fact that the liquid medium contains nanofibrillated cellulose (NFC) in an amount of 200 to 300 g per liter, a reproducible, uniform improvement of the acoustic properties of the resonance wood free from local defects is ensured.