To develop a Fenton reaction catalyst that can maintain divalent iron stably for a long period of time, can utilize trivalent iron or metallic iron, which is an inexpensive iron-supplying source, by converting into divalent iron, and is harmless to the human body and the environment, provided is a Fenton reaction catalyst, including, as an active component, a reaction product obtained by mixing a specific reducing organic substance (e.g., ascorbic acid, a polyphenol-containing plant component, or a plant dry distillation liquid component) with an iron-supplying source at a predetermined ratio 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.
