The present invention relates to quaternary ammonium salts and their use as mold inhibitors. The quaternary salts can be prepared by a chloride ion-promoted reaction between a tertiary amine and an alcohol or polyol in strong acid solution. The quaternary ammonium salts can be applied to a substrate in order to impart anti-mold properties to the substrate. Preferably, the quaternary ammonium salt compounds are applied to paper substrates in an amount of about 1000 ppm. Preferably, the quaternary ammonium salts compounds are applied as mixtures of more than one quaternary ammonium salt compound. The treated substrate does not require encapsulators, binders, or retention aids.