A clean surface of LaB6(210) exhibits the low work function of 2.2±0.1 eV at room temperature. This is lower than those of the (100), (110), and (111) surfaces. Similarly to the (100) surface, La atoms exist in a (1×1) ordered structure at the outermost layer of the (210) clean surface. The value of the low work function of LaB6has been discussed on the basis of those data together with the Lang‐Kohn theory. The changes of the (210) surface with oxygen chemisorption are more analogous to those of the (110) surface than the (100) and (111) surface. Work function changes from 2.2 to 3.1 eV with oxygen exposure and saturates above ∼15 L; the periodicity of the surface‐atomic lattice disappears almost completely.