Abstract: Pristine and transition metal doped Mn3O4 nanocrystals were prepared by a hydrothermal method using KMnO4 and glucose as raw materials.The obtained samples were characterized by X-ray diffraction（XRD），scanning electron microscopy （SEM），transmission electron microscopy（TEM），X-ray photoelectron spectroscopy（XPS），and H2-temperature-programmed reduction（H2-TPR)，and their catalytic activities on CO oxidation were also studied.The results showed that Mn3O4 nanocrys- tals were formed with the elimination of MnOOH impurity phase by doping with transition metal cations.The obtained particles were shaped in octahedron with various sizes according to the doping cations.The catalytic activities of doped Mn3O4 nanocrystals on CO oxidation were greatly enhanced by comparing with pristine Mn3O4，demonstrating the doping effect on nanocatalysts.

Key words: Mn3O4, doping effect, hydrothermal synthesis, catalytic properties, CO oxidation