In this study, we report the synthesis of uniform and narrowly size-distributed ZnO nanoparticles with sizes of approximately 3 nm; the nanoparticles were prepared by means of organic-ligand-assisted hydrothermal conditions with various organic modifiers. The results obtained herein revealed that among the various functional groups tested (alcohols, aldehydes, carboxylic acids, and amines), only hexanol effectively controlled the nucleation and crystal growth of spherical ZnO nanoparticles. The use of hexanol also caused the surface of the ZnO particles to change from hydrophilic to hydrophobic, which would enhance the dispersion of these particles in polymer matrices, paints, cosmetics, and other organic application media.