Anatase Co-doped TiO2 nanoparticles capped by oleic acid with a wide range of dopant concentrations (0-23.27%) were synthesized. The surface chemistry of the doped nanoparticles was probed by Fourier transform infrared spectroscopy and thermogravimetric analyses. An interesting effect of doping was discovered: doping with Co2+ at the nanocrystal surface significantly improves the solubility and dispersibility of the nanocrystals in apolar solvents, which can originate in the change in the self-assembled structure of the surface ligand from the weakly hydrophobic quasibilayer in undoped TiO2 nanorods to the strongly hydrophobic monolayer in Co-doped TiO2 nanocrystals.