Polyimide networks are key in the development of stable, resilient, and efficient membranes for separation applications under demanding conditions. To this aim, the controlled design of the network’s nanostructure and its properties are needed. Yet, such control remains a challenge with the currently available synthesis methods. Herein, we present a simple nanofabrication approach that allows the controlled nanoconfinement, growth and covalent attachment of polyimide (PI) networks inside the mesopores of γ-alumina layers. The attachment of the PI network on the γ-alumina layer was initiated via 2 different pre-functionalization steps who play a pivotal role in inducing the in-situ polymerization reaction at the pore entrance and/or at the inner pore surface. The nanoconfinement was found to be limited to maximal the 1.5 μm thick γ-alumina supporting layer and the resulting hybrid PI/ceramic membranes showed stable performance in a variety of solvents. These PI/ceramic membranes were found to be very efficient in the challenging separation of small organic dye molecules such as Rhodamine B (479 g mol-1) from toxic solvents such as dimethylformamide or dioxane. Therefore, this technique opens up possibilities for a multitude of separations. Moreover, the PI synthesis approach can be applied to other applications that rely on porosity and stability control as well, such as for advanced insulation and anticorrosion.