SBA-15 was synthesised with Pluronic P104 ((EO)27-(PO)61-(EO)27)) as structure promoter at 45°C, with and without NaCl (1.0 M) added to the synthesis mixture. TEOS (tetraethyl orthosilicate) was used as silica source. The formation process was studied by in-situ SAXS/SAXD using synchrotron light. Addition of salt affects the micellar size, initial cell-parameter of the 2-D hexagonal phase (p6mm) as well as the kinetics of the aggregation of the polymer-silica composite. The effects caused by the salt are explained by a general ionic effect. The salt makes the aqueous solution more polar and hence a worse solvent for the polymer. The ethylene oxide chains of the polymer will be more solvophobic. This leads to a larger aggregation number of the micelles as well as to a stronger interaction between them.