Previous products of nano-ZrO2 usually come in the form of transparent sol. The solvent accompanied may not be compatible with the target polymer system, when they are to be used in organic/inorganic composite. We have developed a low temperature hydrothermal crystallization process to produce nano-ZrO2 clusters. The product could be made as re-dispersible fine powders after carboxylic acid modification. By "re-dispersible", we are referring to the situation that a slightly bluish but transparent sol containing more than 10 wt % of ZrO2 could be prepared by adding the powder into a solvent or monomer followed by a few minutes of ultrasonic agitation. The most interesting surface modifiers are methacrylic acid (MA). A dispersion of MA modified ZrO2 could be directly coated on substrate and UV cured into transparent film with refractive index as high as 1.76. It could also be blended with PUA for the preparation of a hard film on PMMA.