Novel fluorinated polymer nanoparticles (PNPs) for F-19 MRI were prepared by living radical polymerization initiated by a dendrimer. The dendritic macroinitiator with Br substituents was synthesized from hydroxy-group-terminated G2 polyamidoamine dendrimers. The arborescent fluorinated polymers of 2,2,3,3-tetrafluoropropyl methacrylate and 2,2,2-trifluoroethyl methacrylate were characterized in molecular weight, the number of arms, the degree of polymerization per arm, and the diameter as a whole. The PNP diameter was precisely controlled by the molecular weight in the range of 3-25 nm. In addition, the fluorinated PNP gave a narrow resonance by F-19 NMR spectroscopy. These results indicate that the fluorinated PNP can be used as a new type of F-19 MRI agent.