Relaxation based MR images have superior spatial resolution compared to other MRI approaches. In addition, structural MRI requires short scan time and yet has high signal to noise ratio. However, the greatest limitation of structural MRI is poor specificity and sensitivity to pathology. Thus a well characterized MR molecular contrast agent would be a major advance. Here we present 3 nm iron oxide nanoparticles (IONP) as a T1 contrast agent. The 3 nm IONP showed strong T1 effects up to 13.5 ms echo time. A fully functionalized 3 nm IONP would be an appropriate component for molecular contrast agents.