Graphene/NiFe2O4 (Gr/NiFe2O4) nanocomposites were synthesized using a facile one-pot hydrothermal method with graphene oxide (GO), Fe2(SO4)3 and NiSO4 as starting materials. The as-prepared Gr/NiFe2O4 was characterized using X-ray diffraction (XRD), transmission electron microscope (TEM), and Raman spectra (RS). The results indicate that GO is reduced to graphene and the well-dispersed NiFe2O4 nanoparticles are simultaneously deposited onto graphene sheets under the conditions generated by the hydrothermal system. There is a strong interface interaction between the graphene and NiFe2O4 nanoparticles, which avoids their aggregation. The formation mechanism of Gr/NiFe2O4 nanocomposites was discussed. The growth kinetics of NiFe2O4 nanoparticles follows the Ostwald ripening, in which smaller particles dissolve owing to their high surface energy and are essentially consumed by larger ones.