We report the longitudinal water proton relaxivities (r1) of several 3d and 3f transition metal oxide nanoparticles. These include ultra small iron oxide, manganese oxide, europium oxide, gadolinium oxide, and dysprosium oxide nanoparticles. The nanoparticles ranged from 1.0 to 3.0 nm in diameter. Ultra small metal oxide nanoparticles with metal ions of high and pure S-state electron magnetic moments showed high r1 relaxivities. The measured relaxivities indicate that ultra small gadolinium oxide nanoparticles with a high r1 relaxivity of 12.6 mM-1s-1 may be suitable for a sensitive T1 MRI contrast agent.