Isothermal vapor-liquid equilibria for hydrogen fluoride + 1,1-difluoroethane at 288.23 and 298.35 K were measured using a circulation type apparatus equipped with an equilibrium view cell. The compositions of both vapor and liquid phases were analyzed by an on-line gas chromatographic method. They were compared with PTx equilibrium data measured by the total pressure method. The experimental data were correlated with Anderko’s equation of state using the Wong-Sandler mixing rule as well as the van der Waals one-fluid mixing rule. The Wong-Sandler mixing rule gives better results, and the relevant parameters are presented.