It has been found that the work function of Mo(100) surface can be reduced to 2.1 eV by heating it with a slight layer of zirconium oxide in a vacuum condition [S. Satoh et al., J. Vac. Soc. Jpn. 47, 143 (2004)]. Here the low work function surface, which is abbreviated as ZrO/Mo(100), was examined aiming to understand the reducing mechanism of the work function. Low-energy electron diffraction is employed to analyze the atomic arrangement at the surface and x-ray photoelectron spectroscopy to identify the surface chemical condition. The experiment gives almost the same results as for the ZrO/W(100) low work function surface. (c) 2007 American Vacuum Society.