Fe-doped SnO2 nanoparticles doped with 5 and 8 mol% were successfully synthesized by a controlled precipitation method. X-ray diffraction (XRD) patterns are consistent with the rutile-type structure. The XRD patterns of thermal-treated samples were analyzed using the Rietveld refinement method. The results are consistent with both the increase of the crystallite size and the disappearance of the residual strain as the temperature of thermal treatment is increased. Meanwhile transmission electron microscopy images corroborate the crystallite size. The analysis of the magnetic measurements suggests the occurrence of superparamagnetism which coexists with a paramagnetic signal.