Magnetic nanobeads are synthesized by coprecipitation of hollow iron oxide nanoparticles and an amphiphilic polymer. The resulting nanobeads can be tuned in diameter and nanoparticle content. X-ray absorption near-edge structure (XANES) spectroscopy and superconducting quantum interferometer device (SQUID) characterization of the nanobeads reveal that they exhibit an increased effective magnetic anisotropy as compared to the individual nanoparticles, despite that no structural changes of the particles had occurred during the embedding process into the polymer. The spinspin relaxation times of the pristine hollow nanoparticles and of the final magnetic nanobeads reveal a high R-2 relaxivity of 206 s(-1) mM(-1) for the magnetic nanobeads. This result should enable their application as negative contrast enhancing agents in magnetic resonance imaging.