The apparent molar volumes, V-phi and apparent molar isentropic compressibilities, K-s,K-phi of three benzyldimethylammonium based protic ionic liquids, namely, benzyldimethylammonium acetate (BDMAA), benzyldimethylammonium propionate (BDMAP), and benzyldimethylammonium hexanoate (BDMAH) in water and ethanol have been determined at T=(293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and at ambient pressure from density, rho and speed of sound, u measurements. The Redlich-Mayer type of equation has been used,to calculate the apparent molar volume, V-phi(infinity) and apparent molar isentropic compressibility, K-phi(infinity) at infinite dilution, and the corresponding empirical parameters (S-v, B-v, S-k and B-k). The negative magnitude of limiting volumetric slopes, S-v versus m(1/2) for (BDMAA + ethanol) binary solutions, suggests that BDMAA-ethanol interactions are strong. Further, the change in thermodynamic properties of binary solutions in relation to the alternation in the anionic structural constitution of protic ionic liquids has also been evaluated. (C) 2014 Elsevier B.V. All rights reserved.