Abstract: The present invention provides a sterilization auxiliary for ozone sterilization which is an aqueous solution including a Component (A) of an aluminum compound which produces aluminum ions in an aqueous solution, and a Component (B) of one or more of acids selected from phosphoric acid, citric acid, malic acid, succinic acid, gluconic acid, lactic acid, and L-tartaric acid, wherein the pH of the aqueous solution is greater than or equal to 1.0 and less than 5.0, and an ozone sterilization method for ozone-treating a substance to be treated using the sterilization auxiliary. According to the present invention, a sterilization auxiliary for ozone sterilization in which a high sterilizing effect may be obtained using less ozone without burdening sterilization apparatus and a substance to be treated, and a low-cost ozone sterilization method using the sterilization auxiliary can be provided.