Ethylmercury (sometimes ethyl mercury) is a cation composed of an organic CH3CH2— species (an ethyl group) bound to a mercury(II) centre, making it a type of organometallic cation, and giving it a chemical formula C2H5Hg+.

In the body, ethylmercury is most commonly encountered as derivatives with a thiolate attached to the mercury.

Given the comparable electronegativities of mercury and carbon, the mercury-carbon bond is described as covalent.[3]: p.

[5] Risk assessment for effects on the human nervous system have been made by extrapolating from dose-response relationships for methylmercury.

[1] Estimates have suggested that ethylmercury clears from blood with a half-life of 3—7 days in adult humans.