This research was designed to examine the thermodynamic properties of aqueous solutions of pyridine and piperidine. The density, excess molar enthalpy of mixing, H-E, and excess molar volume of mixing, v(E) of piperidine-water and pyridine-water mixtures were studied at three temperatures, ranging from 294 K to 315 K. The H-E and v(E) are negative for both mixtures, minimizing at a water mole fraction of about 0.55. The minimum H-E for piperidine-water mixtures is -2.23 kJ/mol which is compared with -1.63 kJ/mol for pyridine-water mixtures. The minimum v(E) are about -1.7 cm(3)/mol and -0.7 cm(3)/mol for piperidine-water and pyridine-water mixtures. respectively. The thermal expansion coefficients alpha(T) at 303 K, calculated from the density studies, exhibited significant positive deviations (about 20%) from ideality for piperidine-water mixtures. In contrast to this pyridine-water alpha(T) only exhibited small positive deviations from ideality of about 2%. The results predict decreases in the absolute magnitude of v(E) with an increase in temperature which are 5. x 10(-3) cm(3)/K mol and 1. x 10(-3) cm(3)/K mol, for piperidine-water and pyridine-water Mixtures, respectively. The results for v(E) for piperidine-water mixtures agree with the very precise work of Afzal et al., J. Chem. Thermodyn. 40 (2008) 47-53. The data are interpreted in terms of the greater number of opportunities for hydrogen bonding interactions between the unlike molecules for the piperidine-water mixtures. (C) 2009 Elsevier B.V. All rights reserved.