Medium effect and equilibrium studies in aqueous solution are reported for dimethyltin(IV) complexes such as 2-(N-morpholino) ethanesulfonic (Mes) and 3-(N-morpholino) propanesulfonic (Mops) acid. Stoichiometries and stability constants of the complexes formed were determined at different temperatures and ionic strength 0.1 M NaNO3. The results showed that the best fit of the titration curves was obtained when complexes ML, MLH-1, MLH -2 and MLH-3 were expected beside the hydrolysis product of the dimethyltin(IV). The thermodynamic parameters calculated from the temperature dependence of the formation constant of the DMT(IV)-Mes and -Mops complexes were investigated. The effect of dioxane as a solvent on the formation constants of DMT(IV)-Mes and DMT(VI)-Mops complexes was discussed. © Published by Elsevier B.V.