Structures of Rh/l AL (atomic layer) GeO2/SiO2 were studied during reduction and oxidation processes by means of in situ XAFS (X-ray absorption fine structure). It was found that RhGe bimetallic particles with Rh-Rh and Rh-Ge distances at 0.266 and 0.242 nm were formed after reduction at 723 K, respectively. Subsequent oxidation at 673 K regenerated 1 AL GeO2 structure on the SiO2 surface. This reversible structure transformation is discussed in relation to reactivity and volatility of Ge oxide species.