Iron (Fe) is an essential trace nutrient for marine phytoplankton growth and is therefore an important regulator of oceanic productivity and marine biogeochemical processes. The South China Sea (SCS) is a typical oligotrophic marginal sea, where energetic hydrodynamic events, such as internal waves and sub-mesoscale eddies, facilitate the transport of shelf sediments into the deep basin. However, the cross-shelf transport of sedimentary Fe remains poorly constrained, limiting our understanding of Fe cycling in the SCS. In this study, dissolved Fe (dFe) concentration and ²¹⁰Po–²¹⁰Pb disequilibrium were analyzed at two stations, A2 (118°21′21″ E, 20°59′05″ N) and SEATs (115°48′11″ E, 18°03′25″ N), in the northeastern SCS during the KK1802 cruise onboard the R/V Tan Kah Kee. The results showed anomalously high dFe concentrations in the intermediate waters of the northeastern SCS, accompanied by deficits in ²¹⁰Po relative to ²¹⁰Pb, indicating the contribution of lateral sediment transport. Based on preformed dFe concentrations and intermediate water transport in the SCS, the input flux of sedimentary dFe to the intermediate waters of the northeastern SCS basin was estimated to be 13.8 ± 4.8 μmol m⁻² d⁻¹. Furthermore, using the ²¹⁰Po–²¹⁰Pb disequilibrium approach, together with the Fe content and Fe solubility of shelf sediments, the dFe flux released through particle dissolution during lateral sediment transport was estimated to be 4.56 ± 0.09 μmol m⁻² d⁻¹, accounting for approximately one third of the total sedimentary dFe input. Considering the net outflow of SCS intermediate water through the Luzon Strait, dFe released from shelf sediments is likely transported into the northwestern Pacific Ocean, where it may partially alleviate Fe limitation.