In this study, a series of Na-Zr/TiO2 photocatalysts with different Na contents were synthesized via the sol gel process. The characterization of the materials showed that Na addition facilitates the maintenance of anatase and excess Na led to particle size increases because of the formation of Na2Ti3O7. The XPS results suggested that Na loading can increase the number of oxygen vacancies, leading to more abundant surface hydroxyl groups. The enhanced photocatalytic activities under visible light irradiation can be attributed to a decreasing band gap and increasing oxygen vacancies. The efficiency of the Na-Zr/TiO2 samples was investigated by the degradation of formaldehyde under visible light. A high degradation rate of formaldehyde of approximately 96.6% was obtained with 2.5 mol % Na added to the Zr/TiO2 samples.