Abstract: Methylmercury is a kind of organic mercury with strong bioavailability and toxicity. Because of high bioaccumulation and bioavailability, methylmercury can pose serious harmful effects to aquatic life at higher trophic levels and cause neurotoxicity, endocrine disruption and reproductive toxicity to vertebrates. The presence of methylmercury has been detected in various environmental media (water, sediments and organisms) in China. The traditional water quality criteria for methylmercury was only derived from the acute and chronic toxicity data of aquatic organisms in water that did not take bioaccumulation and bioavailability into account, which may cause lower-protection problem to aquatic ecosystem. As the tissue concentrations could directly reflect the bioavailability of cumulative substances, water quality criteria deriving from toxic data based on tissue was more scie.pngic, and could provide protection for aquatic ecosystem more reasonably and reliably. Based on a review of the latest toxic data for methylmercury exposure, the criteria value of methylmercury based on tissue concentration was calculated at 23.15 μg/kg, the water quality criteria for protection of aquatic life was determined at 0.12 ng/L, and the water quality standard value of methylmercury of aquatic organisms suitable for Chinese aquatic environment was derived at 0.35 ng/L. The results can provide a new method and support for the transformation of methylmercury water quality criteria to the water quality standards and for the water environmental management of bioaccumulative chemicals.