Complexation of methylmercury(II) by sulfate, selenate, carbonate, sulfite, selenite, thiocyanate, selenocyanate, sulfide, and selenide in aqueous solution has been studied by proton magnetic resonance and Raman spectroscopy. Formation constants were determined for the SO42−, SeO42−, CO32−, SO32−, SeO32−, SeO3H−, SCN−, and SeCN− complexes from the pH dependence of the chemical shift and the 199Hg−1H spin–spin coupling constant of the methyl group of CH3Hg(II) in solutions containing both CH3Hg(II) and ligand. The chemical shift and the 199Hg–1H spin–spin coupling constant of the CH3Hg(II) in each of the complexes were also obtained from the same measurements. Proton magnetic resonance parameters were measured for several complexes with sulfide and selenide. The ligand donor atom in each of the complexes was identified using the formation constants, the 199Hg–1H spin–spin coupling constant of the complexed methylmercury and the Raman spectral data. It is of particular interest that, in the selenite complex, the methylmercury is bonded to an oxygen atom whereas sulfur is the donor atom in the sulfite complex.