A protic ionic liquid, bis(2-hydroxyethyl)methylammonium formate, (BHEMF), was synthesized and characterized. The density and surface tension of the protic ionic liquid were determined in the temperature range of 293.15-343.15 K. The molar volume and surface entropy were estimated from the experimental density and surface tension data, respectively. In terms of Glasser's theory, the standard molar entropy and lattice energy of the protic ionic liquid were estimated. Using the methods of Kabo and Rebelo, the molar enthalpy vaporization of the protic ionic liquid, lδg H0m (298.15 K) at 298.15 K and lδ H0m (Tb), at the hypothetical normal boiling point were estimated, respectively. According to the interstical model, the thermal expansion coefficient of the protic ionic liquid, α, was calculated and the result is in very good agreement with the experimental value. © 2012 Springer Science+Business Media New York.