Physicochemical properties were evaluated for polyion complex micelles (PIC), which were prepared from TiO2 nanoparticles and polyallylamine bearing poly(ethylene glycol) grafts (PAA-g-PEG). The zeta potentials of PIC micelles prepared using PAA-g-PEG with different molecular weights of PEG grafts were measured in different aqueous media (i.e., water, phosphate buffer, and Tris/HCl buffer). The PIC micelles in phosphate buffer and Tris/HCl buffer exhibited quite different zeta potentials despite the same salt concentration (10 mM) of the buffer solutions. More specifically, the zeta potential of the FTC micelles in phosphate buffer was effectively neutralized owing to counteranion condensation effects. The onset of counterion condensation into the PIC micelles was dependent on the valence of the anionic molecules and the ability of the PIC micelles to entrap multivalent anionic molecules. Furthermore, as confirmed by laser confocal microscopy observation, multivalent anionic molecules could be delivered to cultured cells through entrapment in the PIC micelles based on multivalent anion condensation effects.