An organic salt of the present disclosure contains terephthalic acid and at least one kind of primary alkylamine. An alkyl group constituting the primary alkylamine has 6 or more and 17 or less carbon atoms. The organic salt of the present disclosure can be used to detect a hydroxy radical contained in a gas, for example. The present disclosure provides: an organic salt that makes it possible to detect a hydroxy radical more easily as well as to detect a hydroxy radical generated in a living body; and a hydroxy-radical sensor adopting the organic salt.