In this study, we report on the effect of γ-Al2O3 nanoparticle (NP) addition into liquid electrolyte for Dye-sensitized Solar Cell (DSC) application. γ-Al2O3 was prepared by a fast ultrasound-assisted sol-gel procedure allowing the formation of γ-Al2O3 crystals with nanometric size and high specific surface area. A quasi-solid state electrolyte was prepared by dispersing 5 wt% of γ-Al2O3 NPs in commercially available electrolytic solution, and optical and electrical properties were analyzed and compared to the bare liquid electrolyte. DSCs were fabricated exploiting NP-based electrolyte and fully characterized. In comparison with liquid electrolyte-based cells, the quasi-solid ones exhibit the same photovoltaic performances and a noticeable extended stability over the time.