The long-chain ionic liquid (IL) 1-hexadecyl-3-methylimidazolium chloride (C(16)mimCl) was used as a template to prepare porous silica with a two-dimensional hexagonal p6mm mesopore structure (MCM-41-type) as well as with a cubic Ia3d (gyroid, MCM-48-type structure) framework in basic synthesis medium via a hydrothermal synthesis procedure. A systematic study was carried out addressing the influence of the relative concentration of the IL and the pH on the mesostructure. As a main result, the IL template shows a broad range of conditions that allow the synthesis of the gyroid mesostructure with improved reproducibility. Unexpectedly, the formation of the hexagonal phase is less favorable, as the latter is quite sensitive to variations in parameters. This preference for the bicontinuous structure can be attributed to the special headgroup packing of ILs containing imidazolium groups.