The dissociation constants of protonated monoethanolamine, N-methyldiethanolamine have been determined in aqueous mixtures of methanol, t-butanol-water and sulfolane solvents. The mole fractions of the organic compounds ranged from (0.2 to 0.95) and the temperatures from (283 to 353)K. Standard state thermodynamic properties like Delta rG, were derived from the results. The basic strength of the protonated alkanolamine decreased with decreasing dielectric constant and increase in temperature of the solvent. (C) 2013 Elsevier B.V. All rights reserved.