A versatile and promising organic–inorganic hybridization method is proposed for the fabrication of highly transparent polystyrene (PSt) and poly(methyl methacrylate) (PMMA) hybrid bulk materials containing highly crystalline ZrO2 nanoparticles (NPs) having a number-average diameter of 3.11 nm. The two key technologies that have been developed are the surface treatment, hydrophobization, and functionalization of ZrO2 NPs originally dispersed in water and their nanodispersion into a polymer continuous phase without any coagulation and/or agglomeration. A unique and fascinating surface treatment method is demonstrated in which the hydrophobization and phase transfer of ZrO2 NPs from water to toluene is simultaneously achieved. Transparent surface-modified ZrO2 nanodispersions in toluene are obtained by a gentle solvent exchange from a ternary solvent mixture composed of water, toluene, and methanol. The addition of carboxylic acids having more than four carbon atoms as the surface treatment agent enables th...