Nonaqueous and aqueous mixtures of methyldiethanolamine and monoethylene glycol form promising absorbents for the combined hydrogen sulfide removal and hydrate control, necessary in natural gas processing. In this direction, the density and viscosity of the binary and ternary systems were measured and modeled in the temperature range of T = 283.15−353.15 K and at ambient pressure. Excess molar volumes and viscosity deviations from ideality were also calculated. The water content varied from 5 to 50 wt % and the amine content from 5 to 90 wt %. Both density and viscosity were modeled using nonrandom two-liquid-based models. Regarding the density modeling, the average absolute relative deviations (AARDs) were found to be less than 0.4% for the binary subsystems and equal to 0.3% for the ternary system. Viscosity modeling results show higher AARD, though always lower than 3.0% for both binary and ternary solutions.