The osmotic coefficients and densities of aqueous and CCl4 solutions involving 18-crown-6 (18C6) as solute in the concentration range 0.1 to 2.0 m at 25 degreesC were measured. The data obtained is used to calculate activities of solvent and activity coefficient of solute and solvent at 25 degreesC as a function of concentration. It has been observed that activity coefficient of 18C6 increases with increase in concentration of 18C6 while the reverse is true for CCl4 solutions. Using the partial molar volume of the solute at infinite dilution, the solute-solvent cluster integral values were evaluated which yielded information on solute-solvent interaction. Application of McMillan-Mayer theory enabled us to obtain second and third virial coefficients for solute, which have been decomposed into attractive and repulsive contributions to solute-solute interactions. These are compared with other solutes such as sucrose, glucose, urea, etc. On the basis of attractive and repulsive contributions to solute-solvent and solute-solute interactions in aqueous solutions, the results are interpreted in terms of hydrogen-bonding of water molecules in the crown cavity and hydrophobic stacking interactions mediated through water molecules. The results of CCl4 solutions are further examined from the point of view of effect of conformational characteristics of 18C6 on the properties in a nonaqueous solvent.