Using a sol-gel process, we have prepared bioactive organic-inorganic hybrid coatings based on epoxy siloxane sols modified with detonation nanodiamond. The microstructure of the coatings was studied by scanning electron microscopy. The coatings were tested - under both laboratory and urban conditions - for bioactivity against the mold fungi most frequently encountered in the air in large cities. The results suggest that such coatings are potentially attractive for protecting historic monuments from biodeterioration.