Ionic liquids (ILs) have been used as the template/structure-directing agent (SDA) for the synthesis of crystalline materials, including aluminophosphates, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). This work unravels the structure-directing role of the imidazolium in ILs in 10-membered-ring zeolite synthesis. Herein, we report the key IL structure-dependent parameters affecting the synthesis of TON and MFI zeolites with one-dimensional (1D) and three-dimensional (3D) channel structures, respectively. The imidazolium dictates the resulting zeolite type and the morphologies of the TON and MFI zeolites are predominantly influenced by both the cations and the silica sources. The structure-directing properties of ILs are supported by the lowered energy state determined by density functional theory (DFT) calculations.