Pyrite is widely distributed in estuarine sediments as an inexpensive natural Fenton-like reagent, however, the mechanism on the hydroxyl radical (HO^·) production by pyrite under estuarine environmental conditions is still poorly understood. The batch experiments were performed to investigate the effects of estuarine conditions including aging (in air, in water), seawater anions (Cl^-, Br^- and HCO₃^-) and light on the HO^· production by pyrite oxidation. The one-electron transfer dominated the process from O₂ to HO^· induced by oxidation of pyrite. The Fe (oxyhydr)oxide coatings on the surface of pyrite aged in air and water consumed hydrogen peroxide while mediating the electron transfer, and the combined effect of the two resulted in a suppression of HO^· production in the early stage of aging and a promotion of HO^· production in the later stage of aging. Corrosion of the surface oxide layers by aggressive anions was the main reason for the inhibition of HO^· production by Cl^- and Br^-, and the generation of Cl^· and Br^· may also play a role in the scavenging of HO^·. HCO₃^- increased the average rate of HO^· production through surface-CO₂ complexes formed by adsorption on the surface of pyrite. The significant enhancement of HO^· production under light was attributed to the formation of photoelectrons induced by photochemical reactions on pyrite and its surface oxide layers. These findings provide new insights into the environmental chemical behavior of pyrite in the estuary and enrich the understanding of natural remediation of estuarine environments.