The structure change of a Cr-Si-O thin film with regard to heat-treatment was investigated not only by the transmission XAFS method but by the surface sensitive XAFS method using synchrotron radiation. As a result of transmission XAFS, the Cr-Si-O thin film as sputtered has an amorphous structure like a mixture of SiO2, Cr and CrSix. After heat-treatment to 650 K, Si-Cr bonds decreased and Si-O and Cr-Cr bonds increased. CrSix is unstable in the system. The interfacial studies by the surface XAFS method showed i) at the interface with polyimide, there is a thin layer which is dominantly made of Cr2O3 and ii) at the interface with Al, Cr atoms are mainly coordinated to Cr. Analyses by the XAFS method gave consistent results with chemical analyses by x-ray photoelectron spei roscopy and observation by transmission electron microscopy.