The density and viscosity of aqueous solutions of N-methyldiethanolamine were measured over the temperature range 60-100-degrees-C. The density and viscosity of aqueous solutions of diethanolamine and diethanolamine + N-methyldiethanolamine were measured over the temperature range 20-100-degrees-C. The surface tension of aqueous solutions of the above mixtures was measured over the temperature range 20-80-degrees-C. The concentration ranges were 10-50 mass % N-methyldiethanolamine, 10-30 mass % diethanolamine, and 50 mass % total amine concentration with mass ratios of 0.0441-0.5883 (diethanolamine to N-methyldiethanolamine). The measured quantities were found to be in agreement with the literature where data were available.