Provided is a Fenton reaction catalyst which can maintain iron in a divalent state for a long period of time. Also provided is a Fenton reaction catalyst which is different from a conventional Fenton reaction catalyst in the point of capable of using trivalent iron (inexpensive iron-supplying source) by reducing into divalent iron. Also provided is a Fenton reaction catalyst including a reaction product as an active component, in which the reaction product is obtained by using roasted and ground coffee beans (in particular, coffee grounds) or tea leaves (inparticular, tea dregs) as feedstocks for supplying a component having a reduction effect, and mixing the feedstocks for supplying the component having a reduction effect with an iron-supplying source containing divalent or trivalent iron in the presence of water. Also provided are a sterilization method, a pollutant degradation method, and a luminescence method based on chemiluminescence, which involve using the Fenton reaction catalyst to thereby generate hydroxy radicals from hydrogen peroxide.
