In this work, the {1-butyl-1-methylpiperidinium dicyanamide, [BMPIP][DCA], or 1-butyl-1-methylpyrrolidinium dicyanamide, [BMPYR][DCA] (1) + water (2)} binary systems were studied as an alternative working pair for the absorption heat pump cycle. The thermodynamic properties of the tested systems including: density, viscosity and (vapor + liquid) phase equilibria were measured as a function of temperature and composition at ambient pressure. The density and dynamic viscosity have been measured at temperature range from (298.15 to 343.15) K. From experimental data, excess molar volumes, V-m(E) and dynamic viscosity deviations, Delta eta were calculated and correlated using Redlich-Kister equation. The isothermal (vapor + liquid) phase equilibria have been measured by an ebulliometric method within temperature range from (328.15 to 368.15) K and pressure range from (0 to 100) kPa. The excess enthalpies for the tested systems were determined at T = 298.15 K using isothermal titration calorimeter. NRTL equation was used to correlate (vapor + liquid) phase equilibria and excess enthalpy. The influence of the cation structure on the presented physicochemical and thermodynamic properties were discussed. (C) 2013 Elsevier Ltd. All rights reserved.