Raman spectroscopy was used to study structural changes, in particular, the formation of contact-ion pairs in supersaturated aqueous NaCH3COO and Mg(CH3COO)(2) droplets at ambient temperatures. The single, droplets levitated in an electrodynamic balance (EDB), lost water, and became supersaturated when the relative humidity (RH) decreased. For NaCH3COO droplet the water-to-solute molar ratio (WSR) was 3.87 without solidification when water molecules were not enough to fill in the first hydration layer of Na+, in favor of the formation of contact-ion pairs. However, the symmetric stretching vibration band (v(3) mode) of free -COO- constantly appeared at 1416 cm(-1), and no spectroscopic information related to monodentate, bidentate, or bridge bidentate, and acetate ion. On the other contact-ion pairs was observed due to the weak interactions between the Na+ hand, the band of methyl deformation blue shifted from 1352 to 1370 cm(-1) (at RH = 34.2%, WSR = 2.43), corresponding to the solidification process of a novel metastable phase in the highly supersaturated solutions. With further decreasing RH, a small amount of supersaturated solution still existed and was proposed to be hermetically covered by the metastable phase of the particle. In contrast, the interaction between Mg2+ and acetate ion is much stronger. When WSR decreased from 21.67 to 2.58 for the Mg(CH3COO)(2) droplet, the band of C-C-symmetric stretching (v(4) mode) had a blue shift from 936 to 947 cm(-1). The intensity of the two new shoulders (similar to1456 and similar to1443 cm(-1)) of the v(3) band of free -COO- at 1420 cm(-1) increased with the decrease of WSR. These changes were attributed to the formation of contact-ion pairs with bidentate structures. In particular, the small frequency difference between the shoulder at similar to1443 cm(-1) and the v(3) band of the free -COO-group (similar to1420 cm(-1)) was proposed to be related to the formation of a chain structure based on the contact-ion pairs of bridge bidentate. The continuous formation of various contact-ion pairs started at higher WSR value (WSR = 15.5) greatly reduced the hygroscopic properties of Mg(CH3,COO)(2) droplet, so that the WSR of Mg(CH3COO)(2) droplets was even lower than that of NaCH3COO in the RH range of 40-60%.