Nanoparticles start to be very popular over the last decade. What are these tiny materials? A nanoparticle (or nanopowder or nanocluster or nanocrystal) means that a microscopic particle. It was at least one dimension less than 100 nm. Several area such as biomedical, optical, and electronic fields use these materials in wide variety of potential applications. Current several scientific research mainly concentrated on these materials. Since their size are nearly nanoscale and as the percentage of atoms at the surface of a material becomes significant the properties of materials change. Moreover,when it was compared with the bulk material, nanoparticle exhibits a number of special properties. Another key property is that nanoparticles have a very high surface area to volume ratio.Thanks to this property, nanoparticles have a tremendous driving force for diffusion ability, especially at elevated temperatures. They also have unique optical properties. Nanoparticles often possess unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. Besides these very important properties, suspensions of nanoparticles are possible. This property is very important and necessary for chemical studies. Since the interaction of the particle surface with the solvent is strong enough to overcome density differences, which otherwise usually result in a material either sinking or floating in a liquid. Finally, nanoparticles with one half hydrophilic and the other half hydrophobic are named as “Janus particles” and are particularly effective for stabilizing emulsions. They can self-assemble at water/oil interfaces and act as solid surfactants. To sum up, nanopartiles can be called as the materials of 21st century . Therfore, scientific research on nanoparticles is intense as they have many potential applications in medicine, optics, and electronics.