Abstract: The ultrasonic velocity, density and viscosity have been measured for the mixtures of alkanols, namely, 1-propanol, 1-butanol and 1-pentanol with chlorobenzene in toluene at 303 K. The experimental data have been used to calculate the acoustical parameters namely adiabatic compressibility (β), free length (Lf), free volume (Vf) and internal pressure (πi). The excess values of some of the above parameters are also evaluated and discussed in the light of molecular interaction present in the mixtures. Existence of strong molecular association is observed in the present study. Such a molecular association is found to be by hydrogen bonding through dipole-dipole interactions. Also, donor-acceptor complexation is observed in the present investigation. It is interesting to note that the hetro and homo association of molecules decreases with increasing chain length of the carbon atom in alkanols.