The purpose of this study was to clarify the specific information requirements for target laypeople in Japan to facilitate their understanding and judgment regarding the health risks of mercury in fish. In this study, we created mental models of experts and non-experts with regard to the health risks of mercury and compared the two models to analyze gaps in important knowledge and misunderstanding of the health risks involved. The non-experts were 24 females who participated in interviews. The results suggest that the non-experts are continually confusing their knowledge about the Minamata disease with the present situation. They assume that serious and incurable congenital and acquired diseases occur from a cumulative accumulation of mercury in the body resulting from high consumption of seafood contaminated by factory effluent. Public information should be focused on the relationship between body accumulation and half-life, and the health effects of low-dose mercury exposure.