We demonstrate a single-step facile approach for highly water stable assembly of amine-functionalized Fe(3)O(4) nanoparticles using thermal decomposition of Fe-chloride precursors in ethylene glycol medium in the presence of ethylenediamine. The average size of nanoassemblies is 40±1 nm, wherein the individual nanoparticles are about 6 nm. Amine functionalized properties are evident from FTIR, thermal and elemental analysis. The saturation magnetization and spin-echo r(2) of the nanoassemblies were measured to be 64.3 emu/g and 314.6 mM(-1)s(-1), respectively. The higher value of relaxivity ratio (r(2)/r(1)=143) indicates that nanoassemblies are a promising high efficiency T2 contrast agent platform.