Minamata disease is a well-known mercury contamination that happened in Japan in 1953. Due to demand during world war, second mercury disaster occurred in Niigata Prefecture in 1965. This is a review on the Niigata Minamata disease based on available documents and local expert opinions on the disaster. The aims of this paper are to record exposure history like the source of mercury in Agano River and specific fish that was associated with the disease. It is for an appraisal of the basic mercury exposure control, particularly to protect Japanese and world population during that time. There was indication that initial exposure limit for mercury was calculated incorrectly, and higher safe dose was applied. This epidemiological study is very useful and significant in comprehend the correct estimation of the human exposure to any hazardous substances.