Abstract: Compositions for the protective treatment of wood against rot and attack by insects which comprise at least the following components: a) 10-90 parts of coal-tar oil b) 2-20 parts of a biocidally active quaternary ammonium compound c) 10-90 parts of water. are described. The compositions according to the invention are easily preparable stable emulsions which are distinguished, inter alia, by good penetrability, strongly reduced odour of the treated woods, absence of annoying tar oil enrichments at the surface and strongly reduced “bleeding” of the treated wood at hot temperatures, considerably enhanced activity in spite of a lower coal-tar oil content and reduced toxicity compared to pure coal-tar oil.