Gel polymer electrolytes (GPEs)-based on poly(methyl methacrylate) PMMA and propylene carbonate (PC) with LiClO4 or NaClO4 salt are prepared using either the commercial product Superacryl® or directly from the monomer and AIBN (2,2′-azobis(isobutyronitrile)) initiator. The nanostructured aluminum oxide is added to the mentioned systems in various ratios. Solutions of liquid PC–perchlorate and polymer electrolytes are compared with focus on ionic conductivity. The ionic conductivity of polymer-based electrolytes is significantly influenced (of almost by one half order of magnitude at room temperature) by the addition of nanosized Al2O3. On the contrary, the conductivity of liquid electrolytes is decreased by the addition of alumina in the blend. A slight enhancement of mechanical properties is observed.