The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (e _cb ⁻ ) and hole (h ⁺ ). The conduction band electron (e _cb ⁻ ) reacted with an electron acceptor, methylviologen dichloride hydrate (MV ²⁺ ), forming reduced methylviologen (MV ⁺ ) with a second-order rate constant of (2.6 ± 0.3) × 10 ⁹ L mol ⁻¹ s ⁻¹ . The concentration of MV ⁺ was strongly influenced by MV ²⁺ initial concentration and pH values. The flat band potential of goethite was calculated to be E _fb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.