Human exposure to nano-sized particles (NSP) has increased over the last century with anthropogenic sources, and the rapid development of nanotechnology becomes an another source of such exposure. Information regarding the safety of nanotechnology and its product, nanoparticles, is urgently needed when assuming exposure through inhalation, oral intake, and penetration across skin is ever increasing as growing nanotechnology rapidly. The recent advancement of biokinetic studies with NSP and newer epidemiologic and toxicologic studies with ultrafine particles can be the basis for the nanotoxicology. Some concepts of nanotoxicology can be known from the results of these results. Specific small size of NSP, when inhaled, facilitates deposition by difusional mechanism in all regions of the respiratory tract and uptake into cells, ranscytosis across epithelial and endothelial cells into the blood and lymph circulation to reach target sites. Translocation along axons and dendrites of neuron makes an access to CNS and ganglia. These biokinetics are dependent on NSP surface chemistry. Risk assessments of NSP include appropriate and relevant doses/concentration selections, the increase effects in the organism and the benefits of possible desirable effects. An interdisciplinary team approach is desirable for nanotoxicology research and an appropriate risk assessment.