A prerequisite for using the new geochemical tracer—Fe isotope—to constrain some important geochemical processes lies in the adequate understanding of the process and mechanism of Fe isotope fractionation. This paper presents a review of the current situation of people's understanding of mass fractionation processes at low-temperature environments, which include precipitation, dissolution, reduction, oxidation, adsorption, and biological processes. During the precipitation, the resultant is depleted in heavy Fe and the heavier Fe(Ⅱ) is preferentially adsorbed on the surfaces of Fe(Ⅲ)(hydr)oxides. When different kinds of valencestatecoexist, heavy isotope is preferentially enriched in high-valence state.