The need for more sustainable energy sources has accelerated research into bio-oil as a potential fossil fuel substitute. Nevertheless, several drawbacks hinder the direct use of raw bio-oil produced from biomass pyrolysis as a fuel for transportation, such as its high oxygen concentration, acidity, instability, and low heating value. The unique surface features, high catalytic activity, thermal stability, and tunable physicochemical properties of nano metal oxides have made them extremely useful catalysts for the upgrading of bio-oil. Using nano metal oxides, including TiO2, ZnO2, CeO2, Al2O3, ZrO2, zeolite, and Fe2O3, this chapter examines the basic mechanisms by which they improve the deoxygenation, cracking, and hydrogenation processes in bio-oil upgrading. Particular focus is placed on how particle size, surface acidity/basicity, and nanostructure morphology affect catalytic performance. The chapter also discusses current developments in nano metal oxide-based catalytic pyrolysis, hydrodeoxygenation, and emulsification processes, emphasizing their benefits over traditional catalysts. There is also discussion of difficulties including regeneration, catalyst deactivation, and economic viability. The knowledge presented here aids in the creation of effective catalytic systems for the long-term, sustainable production of premium biofuels.