The aggregation and dispersion behavior control of nanoparticles in liquid is one of the most important technology and science for the application of nanoparticles in various fields ; for examples, materials, medicals, printing and cosmetics etc. In this report, the reasons and mechanism of the difficulty to control the dispersion behavior were introduced, firstly. Then, based on the discussion of aggregation mechanism, two kinds of approach for the dispersion in liquid were reviewed. One is surface modification after the preparation of nanoparticles, and the other is simultaneous process of nanoparticle preparation and dispersion control. By using both approaches, it is possible to disperse nanoparticle aggregates up to primary particles, if solid concentration is lower than several volume ％ in liquid suspension. The future subjects for the practical application of nanoparticles were finally discussed.

In this study, TiO₂-SiO₂ nano-hybrid particles were prepared by sol-gel process and liquid phase deposition （LPD）. In sol-gel process, the hydrolysis reaction of titanium alkoxide was controlled by acetic acid to attain the TiO₂ nano-coating on the SiO₂ nano particles. In addition, the hybrid particles were dried by under the super critical drying to suppress the hard agglomeration of the as-prepared nano-hybrid sol. In liquid phase deposition, TiO₂-SiO₂ nano-hybrid particles were obtained by control the reaction condition. As a result, uniform TiO₂ nano coating layer on the SiO₂ nano particles was attained. The quantum size effect of the obtained hybrid particles was estimated by ultraviolet-visible spectrum. As a result, the obtained hybrid particles had the quantum size effect, even their particle diameter was sub-micron size.