A promising superparamagnetic nanomagnetite dipped with Gd was synthesized for possible medical applications. Its size and morphology are independent of Gd content ranging from 1 to 5%. Gadolinium (III) replaced Fe(III) in the lattice. The sizes of Gd-doped nanoparticles ranged from 5 to 50 nm and exhibited a pure magnetite mineralogical phase.