The VLE of acetone-water mixtures was studied at 60 degreesC in the absence and in the presence 3 Angstrom and 4 =Angstrom molecular sieves using the Headspace gas chromatographic (HSGC) technique. Good agreement was noticed when the experimental results in the absence of molecular sieves were compared to the van Lar and UNIFAC models' predictions. These results proved the practical feasibility of using the HSGC in measuring the VLE of binary mixtures. The experimental results obtained in the presence of molecular sieves showed that the VLE of acetone-water mixtures was altered significantly in the presence of molecular sieves. A complete separation of acetone was achieved for a feed composition of about 25 mol % acetone. These results suggest the potential use of molecular sieves to alter the VLE of binary mixtures, especially those with close boiling points or systems that have azeotropic points.