The surface chemistry of the Hf terminated hafnium diboride surface is compared with the surface chemistry of Hf metal. The HfB 2 surface was prepared by growing an epitaxial film of HfB 2 on top of a Hf(0001) single crystal substrate. Previous experiments demonstrated that the epitaxial film has the same surface properties as a HfB 2 (0001) single crystal. The reactivity of the Hf and HfB 2 surfaces toward carbon monoxide, diborane, and 1,2-dicarba-closo-dodecaborane were studied with X-ray photoelectron spectroscopy and reflection absorption IR spectroscopy. It was found that the two surfaces display distinctly different surface chemical properties.