A new γ-Fe2O3 MION ferrofluid has been developed with a salt-assisted solid-state reaction.Characterizations show that the ferrofluid is composed of maghemitenanoparticles with a mean diameter of 2.7 nm. Though the nanoparticles areultrafine, they are well crystallized, with a saturation magnetization value of34.7 emu g−1, making them suitable for MRI applications. In spite of the absence of anysurfactant, the ferrofluid can be stable for more than 6 months. An in vitrocytotoxicity test revealed good biocompatibility of the maghemite nanoparticles,suggesting that they may be further explored for biomedical applications. NMRmeasurements revealed significantly reduced water proton relaxation timesT1 and T2. The MR images of the nanoparticles in aqueous dispersion were investigated using a 3 Tclinical MR imager. These preliminary experiments have demonstrated the potential of theas-synthesized ultrafine, cap-free maghemite MIONs in functional molecular imaging forbiomedical research and clinical diagnosis.