The hydrolysis of (CH3Sn2+ was studied potentiometrically, in different aqueous media (sodium and tetramethylammonium chlorides, sodium nitrate, sodium perchlorate, and sodium sulfate), in a wide range of ionic strength, at t = 25 degrees C. Least squares calculations are consistent with the formation of the species [M(OH)](+), [M(OH)(2)](0), [M(OH)(3)](-), [M(2)(OH)(2)](2+), and [M(2)(OH)(3)](+), with M = (CH3Sn2+. The dependence on ionic strength for different salt solutions was taken into account by using a Debye-Huckel type equation. Medium effects were explained by considering the formation of the chloride and sulfate complexes, [(CH3)(2)SnCl](+), [(CH3)(2)SnCl2](0), [(CH3)(2)Sn(OR)Cl](0), [(CH3)(2)Sn(OH)(2)Cl](-), [(CH3)(2)Sn(SO4)](0), [(CH3)(2)Sn(SO4)(2)](2-), [(CH3)(2)Sn(OH)(SO4)](-), and [(CH3)(2)Sn(OH)(2)(SO4)](2-). Thermodynamic hydrolysis constants of (CH3Sn2+ and formation constants of the complex species with chloride and sulfate ions are reported.