Dynamic changes of standardized mercury concentration in fish taken from the Second Songhua River were evaluated from 1973 to 1991. It decreased 82.6% during this period. And, mercury intake of fish-consuming population and its source were studied. The results proved mercury concentration accumulated in some of the high risk population in 70's came up to and exceeded the threshold for chronic methylmercury poisoning. But, since 1983 mercury level in human body has been dropping greatly, and now falls down below the safety limit. The above facts showed mercury contamination in the Second Songhua River has been under control. But, fish intake should be still limited to appropriate amount to prevent from risk of poisoning.