The chemistry of iron in the oceans plays an important role in controlling primary production and serves a limited micronutrient element for planktons in “biological pump”, and consequently Fe is corresponding potential for regulating global climate by fertilizing the ocean and drawing down atmospheric CO₂. In recent years, the development in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) have improved precision for iron isotope measurements, and therefore both the isotope composition of iron and isotope fractionation effects have been proved useful in tracing the processes that control inputs and outputs of Fe in the ocean and paleoceanographic evolution. This review summarizes our present knowledge of iron isotope geochemistry which documents the Fe isotope composition in various Fe reservoirs of marine systems, and the main Fe isotope fractionations produced by reaction between hydrothermal fluids and mid-ocean basalts and between seawater and submarine basalts, and the Fe isotope composition in various stages of ancient marine sedimentary environments. Furthermore, our review shows that Fe isotope occur significant fractionation in marine systems and light Fe isotope have higher removal activity than heavy Fe isotope. Finally, we highlight the fact that determining the Fe isotope fractionation factor among various mineral, various phases and during biochemical cycling will be an important future avenue of research, which will bear on our understanding of isotopic variations of Fe in both ancient and modern marine sedimentary environments.