The present study is a theoretical investigation of natural convective heat transfer of nanofluids, inside a vertical enclosure, in the presence of a uniform magnetic field. A modified Buongiorno's model is employed for the nanofluid, which fully accounts for the effect of nanoparticle migration. The behavior of the nanofluid is investigated for two different nanoparticles in the water-base fluid, namely alumina and titania. It was observed that the nanoparticles move from the heated walls (nanoparticles' depletion) toward the cold wall (nanoparticles' accumulation) and construct a non-uniform nanoparticle distribution. The results also indicate that for smaller nanoparticles, the nanoparticle volume fraction is more uniform and there is no abnormal variation in the heat transfer rate. Moreover, Nu(B) is reduced in the presence of the magnetic field for alumina/water nanofluid; however, for titania/water nanofluid it is vice versa. (C) 2014 Elsevier B.V. All rights reserved.