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 mu g/mL. It can be uptaken by HeLa cells effectively and resulted in the obvious T-2 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. (C) 2013 Elsevier Ltd. All rights reserved.