An efficacy-indicating resin composition comprising a thermoplastic resin, an electron-acceptable organic compound having a volatility and a sparingly volatile electron-donative developable organic compound. The efficacy-indicating resin composition of the present invention has such many excellent characteristics that it is very simple in production, storage, use and the like, can be used in various shapes, and that its available period can optionally be determined in the range of periods of from several hours to several years. Further, it can enable a visual and easy discrimination of the available period.