Earth-abundant oxides are promising candidates as effective and low-cost catalysts for the oxygen evolution reaction (OER) in alkaline media, which remains one of the bottlenecks in electrolysis and artificial photosynthesis. A fundamental understanding of the atomic-scale reaction mechanism during OER could drive further progress, but a stable model system has yet to be provided. Here we show that Fe3O4 single crystal surfaces, prepared in ultrahigh vacuum (UHV) are stable in alkaline electrolytein the range pH 7-14 and under OER conditions in 1 M NaOH. Fe3O4(001) and Fe3O4(110) surfaces were studied with X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy in UHV, and atomic force microscopy in air. Fe3O4(110) is found to be more reactive for oxidative water splitting than (001)-oriented magnetite samples. Magnetite is electrically conductive, and the structure and properties of its major facets are well understood in UHV. With these newly obtained results, we propose magnetite (Fe3O4) as a promising model system for further mechanistic studies of electrochemical reactions in alkaline media and under highly oxidizing conditions.