Rare earth silicate aerogels (1 − x)SiO 2- xLn 2O 3, with Ln = Dy or Er, have been prepared by the sol-gel process, starting from Dy or Er nitrates and TMOS. After an isothermal treatment of the aerogels, transparent glasses resulted when starting from aerogels with an Ln 2O 3 mole fraction x < 0.05. For higher concentrations, the samples remained opaque even after an isothermal treatment at 1300°C for 15 min. From SEM studies, one is able to observe a phase segregation in both (1 − x)SiO 2- xDy 2O 3 and (1 − x)SiO 2- xEr 2O 3 glasses after the isothermal treatment. The (1 − x)SiO 2- xDy 2O 3 sample shows a residual porosity of about 10%.