Sodium aluminosilicate hydrate (N-A-S-H) gels with various Si/Al ratios are the dominant reaction products of geopolymer. However, their solubility products have not yet been fully determined, which hinders further investigation of thermodynamic modelling of geopolymer system. In this work, N-A-S-H gels with Si/Al ratios ranging from 1 to 3 were synthesized using the sol-gel method. The chemical composition of the synthesized N-A-S-H gels was determined by X-ray spectroscopy (XRF) and thermogravimetric analysis (TGA). The gel structure was characterized by X-ray diffraction (XRD). Dissolution experiments were further performed using the synthesized N-A-S-H gels to determine their solubility products. After dissolution, the aqueous concentrations of Na, Al, and Si were quantified by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and the solution pH was measured. It has been shown that N-A-S-H gels with various Si/Al ratios differ in atomistic structures and solubility products. The thermodynamic properties of N-A-S-H gels can be determined from the experimentally derived solubility products at different temperature, which are expected to complement the thermodynamic database.