Isothermal vapor-liquid equilibria(VLE) for the binary systems of acrylonitrile+water, acetonitrile+water, and acrylonitrile+acetonitrile were measured by headspace gas chromatography(H.S.G.C) at 323.15 K. Both aqueous systems have the azeotropic behaviors. Acrylonitrile+water system has an immiscible region approximately between 0.05 to 0.9 of acrylonitrile mole fractions. VLE data were correlated by common g^E models and compared with predicted values by modified UNIFAC group contribution method. Their mean deviations in vapor phase composition were less than 1%. Excess molar volumes(v^E) of the same binary mixtures at 298.15 K showed negative deviation from the ideality. These data were agreed well within 1% mean deviation with Redlich-Kister equation. Partial molar excess volumes at infinite dilution were calculated from the five Redlich-Kister parameters. Precise azeotropic data were measured directly by spinning band distillator for the acetonitrile+water system. The composition of azeotrope by distillation was x₁=0.757 at 323.15 K and 279.9 torr, which was very close to the result, x₁=0.755, by H.S.G.C. The compositions of azeotropes moved to acetonitrile rich region with decreasing the system pressure.