Isothermal vapor-liquid equilibrium (VLE) data were measured for the 1,1-difluoroethane (HFC152a) + isobutene system in the temperature range from 273.15 K to 348.15 K at 15 K intervals. The experiments were carried out with circulating-type apparatus with on-line gas chromatography. The VLE data were well correlated by the Peng-Robinson-Stryjek-Vera equation of state with the Wong-Sandler mixing rules involving NRTL model, and the results show a positive azeotrope at each temperature. (C) 2008 Elsevier B.V. All rights reserved.