Nanotechnology is now widely believed to be one of the most influential techno-sciences of the future. Or at least it is believed that way in most of industrial countries including South Korea. Naturally, the governments of these industrial countries are currently investing a sizable portion of their human and material resources in order to go ahead in this prominent area of research. Consequently, nanotechnology in these countries has become one of the social sectors where reasonable accountability is normally called for. I claim that reasonable accountability of nanotechnology should take into account the risk-perception of citizens as regards nanotechnology as well as its risk itself. Risk-perception could be variable, changeable, and prone to be polarized; still we should pay more attention to public risk-perception because it is clearly effective in mobilizing public movements, objective in the intersubjective way, and legitimate in a democratic society.