This paper presents liquid viscosities for seven binary mixtures of N-methyldiethanolamine + water over the entire composition range at atmospheric pressure for temperatures between 313.15 and 363.15 K. The work includes measurements of kinematic viscosities with three Cannon-Fenske viscosimeters. The viscosity deviations as a function of composition change sign from negative to positive in the water-rich region at 313.15 and 333.15 K. From 353.15 to 363.15 K, viscosity deviations are positive throughout the entire concentration range. A Redlich-Kister-type equation correlates the viscosity deviations.