Sodium germanate glasses containing cobalt oxide were studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (AES) and optical spectroscopy. The XPS spectra of the starting compounds such as GeO 2, Na 2CO 3 and Co 3O 4, from the melts of which glasses were prepared, were measured. The Co 2p spectra in Co 3O 4 had weak satellite lines while these were intense in the glasses. Furthermore in the glasses an increased energy separation between the Co 2 p 1 2 and Co 2 p 3 2 spin-orbit components as compared with the Co 3O 4 was observed. These observations indicated the presence of high-spin cobalt (II) ions in the glasses. Exact identification of the composition of the Co complexes in the glass is beyond the scope of present work. However, of the few possibilities considered here, the formation of the ternary oxide of Co and Ge surrounded by glass matrix has a high probability. Optical absorption spectra were consistent with these proposed structures.