We present the first direct comparison of the dielectric properties of organically modified BaTiO(3) nanocrystals with unmodified BaTiO(3) nanocrystals. Well-defined 6 nm BaTiO(3) nanocrystals were functionalized with n-hexylphosphonic acid (HPA) to give a surface coverage of 2.4 phosphonate groups/nm(2). Chemisorption of HPA to the oxide surface occurs mainly via tridentate bonding of the deprotonated phosphonate, as determined by (31)P MAS NMR, FT-IR, and XPS spectroscopies. The HPA-modified BaTiO(3) (HPA-BaTiO(3)) nanocrystals possess improved dielectric properties, as demonstrated by decreased sensitivity to temperature and frequency for both the dielectric constant and dielectric loss. HPA-BaTiO(3) had a much lower dielectric loss than unmodified BaTiO(3), which also indicates an improvement in the dielectric quality of the material. Such improvements are of potential importance for the fabrication of high energy density nanocomposites.