Polymeric SiO2 and binary SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 sols, for ceramic membrane modification applications, have been prepared by acid-catalyzed hydrolysis and condensation of alkoxides in alcohol. The sols were characterized with small angle X-ray scattering, using synchrotron radiation. Directly after synthesis, the sols were found to consist of weakly branched polymeric structures with typical fractal dimensions of around 1.5 and radii of gyration of ≈2 nm. The aggregation for silica sols obeys the tip-to-tip cluster-cluster aggregation model in the initial stages. Prehydrolysis of TEOS was found to be the best method to synthesize polymeric binary systems. Based on an analysis of film formation from sols consisting of weakly branched polymers, it is expected that consolidation of these polymers will result in microporous materials.