Density, kinematic viscosity, and refractive index of ternary mixtures formed by N-methyldiethanolamine, methanol, and water were measured at temperatures from 293.15 to 323.15 K. Eleven aqueous solutions of methanol with concentrations between 0 and 100% mass were used as the solvent, while the amine concentration varied between 0 and 30% mass. In addition, these properties were also measured for the corresponding binary systems, i.e., methanol + water, N-methyldiethanolamine + methanol, and N-methyldiethanolamine + water, for the same temperature range. The experimental values of density and refractive index were correlated with the concentration by means polynomial equations, where the fitting parameters are temperature-dependent. Viscosity was correlated to temperature using an Arrhenius-type exponential equation, while the Grunberg-Nissan model was used to correlate it to concentration. Finally, excess molar volumes were calculated from the experimental densities, and their values were adjusted by the RedlichKister equation, for binary systems, and the Cibulka equation, for ternary systems.