For magnetic resonance imaging applications,a facile approach for water-soluble dextran coated amorphous Fe–Co nanoalloy was developed.The as-synthesized nanoalloy had a diameter of 9 nm with a narrow size distribution and showed superparamagnetic property with a saturated magnetization (Ms) of 25 emu/g.In vitro cytotoxicity test revealed that it was biocompatible at a concentration below 120 mg/mL.It can be uptaken by HeLa cells effectively and resulted in the obvious T2 effect after internalization.Biodistribution studies in conjunction with inductively coupled plasma-atomic emission spectroscopy (ICP-AES) confirmed that Fe–Co nanoalloy was preferentially accumulated in lung and spleen after intravenous injection for 4 h.In vivo MRI,dextran-coated Fe–Co nanoalloy can serve as a sensitive contrast agent for MR imaging,especially in the spleen,so we believe that it maybe hold great promise for diagnosis of splenic disease by appropriately functionalizing their surface.