The interactions of glycine (gly), glycylglycine (gly-gly), glycylleucine (gly-leu) with drug ampicillin as a function of temperature have been investigated by combination of volumetric and acoustic methods. Densities and speeds of sound of glycine and its dipeptides in aqueous solutions of ampicillin have been measured at T=(305.15, 310.15 and 315.15)K and atmospheric pressure. The apparent molar volume (V-phi), the partial molar volume (V-phi(0)) and standard partial molar volumes of transfer (Delta V-phi(0)) for glycine and its dipeptides from water to aqueous ampicillin solutions have been calculated from density data. Partial molar adiabatic compressibility (K-phi) and partial molar adiabatic compressibility of transfer (Delta K-phi(0)) have been calculated from speed of sound data. The pair and triplet interaction coefficient have been calculated from both the properties. The absorption spectra have also been recorded for present mixtures with the help of UV-visible spectrophotometer. The results have been explained on the basis of competing patterns of interactions of co-solvents and the solute. (C) 2012 Elsevier B.V. All rights reserved.