The vapor liquid equilibrium (VLE) of the aqueous solutions of two imidazolium-based hydrophilic ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) and 1-hexyl-3-methylimidazolium chloride ([Hmim]Cl), were experimentally studied. An activity coefficient model extended for correlation of the VLE data of the aqueous solutions of the hydrophilic ILs was proposed by taking into account the aggregation effects of IL molecules in aqueous solutions. It was shown that the model can effectively present the VLE characteristics of the strong hydrophilic IL solutions in a wide range of temperatures and full range of mole concentration. The vapor pressures of the two binary systems were measured at (283.15 to 403.15) K and (283.15 to 423.15) K, respectively, and in a range of (20 to 80) IL mol %. The tests were performed by using a static constant-volume apparatus with the temperature uncertainty < +/- 10 mK and the pressure uncertainty < +/- 0.04 kPa for the low-pressure range (0 to 40) kPa and < +/- 0.3 kPa for the high-pressure range (40 to 300) kPa. The experimental data were correlated well with the proposed activity coefficient equation and show a good accuracy and consistency.