In the design and analysis on air washer system with pure water, we need to estimate the vapor-liquid equilibrium of related systems. In this study, the vapor-liquid equilibrium for dilute aqueous solutions of volatile weak electrolytes is examined by numerical calculation and experiments. Equilibrium composition in vapor and liquid phase is calculated for NH3-CO2-H2O, SO2-CO2-H2O and NH3-SO2 CO2-H2O systems. Total solute concentration, pH and vapor phase partial pressure of NH3 and SO2 are determined in dilute aqueous solutions from 10(-6) to 10(-3) mol/kg-H2O in 23 degrees C. Equilibrium composition is predicted and is in good agreement with experimental results in each multicomponent aqueous system. As a result, ionic dissociation and Henry＇s constants quoted from Edwards＇ correlation are available even in dilute aqueous solutions of volatile weak electrolytes. These results allow estimate of ionic dissociation and vapor-liquid equilibrium in dilute aqueous solutions of volatile weak electrolytes.