A novel ab initio method (named the generalized London Potential method) has been developed by Homer et al.(6.9) to predict vapour- liquid equilibrium data for binary mixtures. By this approach, the activity coefficients, vapour- phase composition and total vapour pressures of series of different kinds of binary liquid mixtures such as (i) C6H6-CCl4, (ii) cC(6)H(12)-CCl4, (iii) cC(5)H(10)-CCl4, (iv) cC(6)H(12)-C6H6, (v) cC(5)H(10)-C6H6, (vi) C6H6-CH3OH, (vii) C6H6-C2H5OH (viii) cC(6)H(12)-C2H5OH, (ix) CH3OH-C2H5OH, (x) water-C2H5OH are calculated and the result obtained are compared with experimental data. Reasonable agreement is found between predicted and experimental data for only non-polar simple systems.