In situ immobilization remediation has attracted attention due to its effectiveness in treating contaminated sediment. In this study, the effects of three iron oxides with different crystallinities Fe3O4, (alpha + gamma)-Fe2O3, and alpha-Fe2O3 were investigated as potential in situ amendments for Cd remediation in sediment. The three amendments were mixed with the sediment at dosages of 0%, 2%, and 6% (w/w) for 1-56 d of treatment. The changes of the oxidation-reduction potential (Eh) and pH in the treated sediment samples indicated the related mechanism for Cd immobilization. The experimental results showed that when the sediment sample was treated with synthesized iron oxides for 56 d, the TCLP (toxicity characteristic leaching procedure) leachable Cd in the sediment decreased by 29.43-57.26%, and the PBET (physiologically-based extraction test) extracted Cd decreased by 17.22-39.40%. Additionally, (alpha + gamma)-Fe2O3 exhibited better performances than the other iron oxides. The BCR (Community Bureau of Reference) extraction, results suggested that synthetized iron oxides can effectively reduce the mobile fraction and increase the stable fraction of Cd, which in turn reduces the bioavailability of Cd in the sediment. The analysis of the Fe dissolution risk showed that a high dosage Fe3O4 treatment posed a potential threat to the organisms and suggested that the secondary Fe minerals were involved in the Cd immobilization. Overall, this study provides new insight into the potential applications of iron oxides for Cd immobilization in sediment.