Density and refractive index data at 298.15 K, and isobaric vapor-liquid equilibrium (VLE) measurements at 101.3 kPa were reported for four binary systems of methanol, n-propanol, n-butanol, or isobutanol with N-methylpiperazine. Excess molar volumes and refractive index deviations were calculated. The measurement results exhibit no azeotropes for VLE, negative values for excess molar volume, and positive deviations from ideality for the refractive index over the whole mole fraction range. Liquid-phase activity coefficients and vapor-phase fugacity coefficients were estimated taking into account the nonideal nature of the vapor and liquid phases. The VLE data were shown, to be thermodynamically consistent and were correlated by the UNIQUAC liquid-phase activity coefficient model with temperature-dependent parameters.