The catalytic performance of MnO2(x)-CeO2 (x = Mn/Ce molar ratio) and the synergistic effect have been investigated in formaldehyde removal. The results showed that formaldehyde achieved 100% conversion at 60 degrees C for MnO2(1.5)-CeO2, with the gas hourly space velocity = 120 000 mL h(-1) g(cat)(-1). It was lower than the formaldehyde removal temperature of MnO2 (130 degrees C) and CeO2 (170 degrees C). The apparent activation energy for HCHO oxidation with MnO2(1.5)-CeO2 was 34.2 kJ mol(-1). The partial mutual replacement of Mnx+ and Cex+ decreases the crystallite size due to the MnO2/CeO2 interaction. The X-ray photoelectron spectroscopy and the Raman analyses show that the Mn3+/Mn and O-ads/G(latt) ratios and the relative concentrations of oxygen vacancies for MnO2(1)-CeO2 and MnO2(1.5) CeO2 were higher than those of the rest of the catalysts. Thus, the lattice oxygen (O-latt) from CeO2 readily transfers to the oxygen vacancy, achieving O-latt activation to surface-adsorbed oxygen (O-ads).