In the present study, influence of the alkyl group and temperature on the interactions between the carboxylic acid and ionic liquid (IL) mixtures were discussed in term of density and sound velocity measurements. The IL used in this study was 1-butyl-3-methylimidazolium thiocyanate ([BMIM]+[SCN](-)). The density (rho), and sound velocity (u), of the IL, acetic acid, propionic acid, and their corresponding binary systems {[BMIM]+[SCN](-) (x(1)) + acetic or propionic acid (x(2))} have been measured at T = (293.15, 298.15, 303.15, 308.15 and 313.15) K and at p = 0.1 MPa. The excess molar volumes, V-m(E), isentropic compressibility, kappa(s), and deviation in isentropic compressibility, Delta kappa(s), were calculated using experimental density and sound velocity data, respectively. The Redlich-Kister polynomial equation was used to fit the excess/deviation properties. These results are useful for describing the intermolecular interactions that exist between the IL and carboxylic acid mixtures. (C) 2015 Elsevier Ltd. All rights reserved.