Hydration of oceanic crust and mantle peridotite is a critical process for fluid-rock interaction and element exchange within the oceanic lithosphere. Iron, a key redox-sensitive element, is an important tracer for investigating the redox transfer during this process. However, the mobility of iron and its isotopic composition in serpentinizing fluids remain poorly known. Rodingites, generally formed through the metasomatic replacement of gabbro by Ca-rich fluids, are typically associated with serpentinites. They provide an excellent medium for studying the composition of serpentinizing fluids and associated redox transfer. In this study, we report the Fe3+/ΣFe ratios, S contents and Fe isotopic compositions of rodingites and gabbros from the Xigaze ophiolite (southern Tibet), in order to assess Fe mobility and redox transfer during oceanic Ca-metasomatism. Based on mineralogical features and formation temperatures, we classified the rodingites into three types: prehnite rodingites (type I, prehnite-rich and garnet-absent, <200 ℃), prehnite-garnet rodingites (type II, prehnite and garnet-bearing, 200-400 ℃), and garnet rodingites (type III, prehnite absent and garnet-bearing, ca. 400 ℃). The Fe3+/ΣFe ratio of rodingites (0.19–0.85) is higher than that of gabbro protoliths (0.17–0.22). However, the δ56Fe value of rodingites (-0.19‰–0.12‰) is lower than that of gabbros (0.05‰–0.12‰, in the range of MORB). Isocon analysis of Fe content reveals that prehnite rodingites exhibit only a slight decrease in Fe content. Such rodingites have slightly higher Fe3+/ΣFe ratios but lower δ56Fe values than the gabbro protolith. These observations suggest that early serpentinizing fluids contain little Fe at relatively reducing conditions. In contrast, garnet rodingites, which formed at elevated P–T conditions, exhibit significantly higher Fe3+/ΣFe ratios and S contents but much lower δ56Fe values than the gabbro protolith. A significant negative correlation exists between Fe3+/ΣFe ratios and δ56Fe values of rodingites. These results suggest that fluids with light Fe isotopes were released from serpentinite dehydration, most likely in the form of Fe2+–SOx complexes, which play a crucial role in the high P–T rodingitization. Compared with prehnite and prehnite–garnet rodingites, such fluids increased the Fe3+/ΣFe ratios but decreased the δ56Fe values during the formation of garnet rodingite. This study provides important insights into the Fe mobility and redox transfer in the oceanic lithosphere during nascent subduction of Neotethys Ocean, which has great bearing on the redox heterogeneity in subduction zones.