Mesoporous coralloid NaInO2 was prepared through a facile secondary calcination reaction based on mesoporous In2O3. As a binary sodium transition metal oxide containing a layered structure, the application of prepared mesoporous NaInO2 for HCHO oxidation at room temperature was investigated in this study. After 1.0 wt% Pt supported, the sample possessed a high initial removal efficiencies of HCHO up to 91.4% in 15 min, as well as low final residues of less than 5.5 ppm in 60 min. The characterizations indicate that prepared mesoporous NaInO2 has abundant interface structural defects (XRD peak shifting) and substantial BET surface area of 51.9 m(2)/g, which may generate surface oxygen vacancies manifesting as large amounts of chemisorbed oxygen (OC/Ototal as 36.09%). According to the research results, surface oxygen vacancies might help greatly to capture gaseous HCHO molecules, where chemisorbed oxygen being a cofactor for HCHO oxidation, and then the catalyst transformed HCHO into formate, carbonate and finally CO2 indicated by in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) analysis. Overall, this study provided a promising way for designing Pt-supported catalysts for ambient air purification by introducing surface defects (oxygen vacancies) and chemisorbed oxygens.