Nanometer-scale semiconductor and oxide particles are synthesized by solution methods, i.e. emulsion and reverse micelle techniques. Particle sizes are not only controlled by synthesis conditions, but also selected by flotation and filtration. The physical and chemical properties of these particles are analyzed in finding materials functions appeared in nanometer sizes. In particular, II-VI semiconductor particles show high photo-chemical activities, such as photo-catalytic processes. They also show several size and shape dependent stabilities in diameters <2 nm. © 2002 Elsevier Science B.V. All rights reserved.