The objective of this work is to evaluate to structural evolution of silicate gel in function of time and mineral additives. A comparison between fresh and aged silicate gel synthesized by silica and potassium hydroxide was carried out using FTIR, Raman and 29 Si MAS-NMR spectroscopies. Then, different additives such as NaOH, AlOOH, Li2B4O7 and HCl were incorporated in the silica solution. Their effect on the aspect, transparency, Q n polymerization and stability of silicate gels was studied. The structural study has shown that the quantification of Q n species is difficult using FTIR and Raman spectroscopy because of the existence of several contributions in the same spectral region of silicate species. More precise informations were given by 29 Si NMR spectroscopy which has demonstrated the increase of Q 3 species in the detriment of Q 4 revealing the depolymerization of the structure over time. The study of effect of additives reveals that HCl, AlOOH and Li2B4O7 do not permit to improve the stability of the gel due to the formation of several networks. However, promising results of stability and transparency were obtained using NaOH with a molar ratio of former to modifier of 2.52.