KMn/Al2O3 catalysts with different K:Mn molar ratios were synthesized by a facile impregnation method and attempted for CO oxidation. The correlation in between potassium-dopant amount and the structure/catalytic activity of KMn/Al2O3 catalysts were investigated. Doping small amount of potassium (K:Mn mole ratio less than 1:10) to Mn/Al2O3 catalyst efficiently enhanced the catalytic activity of Mn/Al2O3 catalyst. We found that the K1Mn10/Al2O3 catalyst exhibited the best CO oxidation activity with the TOF of 1.5 x 10(-3) s(-1) for 100% CO conversion at 260 degrees C, which is 50 degrees C lower than that on Mn/Al2O3 catalyst. However, excessive amounts of potassium led to beta-to-alpha-MnO2 phase transformation and poor catalytic performance. DFT calculations combined with multiple characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), O-2 temperature-programmed desorption (O-2-TPD) and hydrogen temperature-programmed reduction (H-2-TPR) were performed to provide a deep insight into the K-doping effect. The results suggested that the addition of an appropriate amount of potassium to Mn/Al2O3 catalyst improved the dispersion of manganese oxide, the mobility and reactivity of surface lattice oxygen, thus significantly improved the catalyst activity. (C) 2016 Published by Elsevier B.V.