Abstract: A composition is disclosed comprising a long-chain quaternary ammonium compound and a wood preservative active agent or a mixture thereof. The long-chain quaternary ammonium compound includes at least one alkyl moiety having from 16 to 50 carbon atoms, unsubstituted or substituted with one or more N, O, S, or halogen atoms. A method of treating wood is disclosed, comprising impregnating wood with the above composition in an amount effective to reduce the preservative active ingredient loss in the treated wood or to increase the resistance of the wood to decay. Treated wood and wood products are disclosed comprising wood impregnated with the above composition, including a treatment level of the long-chain quaternary ammonium compound effective to reduce the preservative active ingredient loss in the treated wood or to increase the resistance of the wood to decay.