It is intended to provide a novel indicator for plasma sterilization in which a publicly known azo dye having been employed hitherto in producing indicators for ethylene oxide gas sterilization or heat sterilization is used and which quickly undergoes a color change in the process of low-temperature plasma sterilization using an oxidative gas such as hydrogen peroxide and shows a sharp color change. Use is made of a publicly known azo dye having been employed in the existing indicators for ethylene oxide gas sterilization or heat sterilization together with a compound capable of changing the color thereof which is a compound having a mercapto group or a dithiocarbamyl group and reacting with the azo dye in plasma sterilization to thereby change the color thereof. Moreover, use can be also made of a polyhydric phenol compound or an aromatic carboxylic acid compound as a fading inhibitor for the azo dye having been color-changed in the course of the plasma sterilization so as to facilitate the stabilization of the color change.
