A series of tellurite glasses containing MoO 3 with the nominal composition x(MoO 3 )-(1 À x)(TeO 2 ), where x = 0.10, 0.20, 0.30, and 0.40, have been investigated using X-ray photoelectron spectroscopy (XPS) and temperature-dependent magnetization techniques. The Te 3d core level spectra for all glass samples show symmetrical peaks at essentially the same binding energies as measured for TeO 2 oxide and with full-widths at half-maximum (FWHM) that do not vary with increasing MoO 3 . These features indicate that the chemical environment of the Te atoms in the glasses does not vary significantly with the addition of MoO 3 and that the Te ions exist in a single configuration, namely TeO 4 trigonal bipyramid (tbp). The O 1s spectra, however, show asymmetry for samples with composition x 6 0.30 and are subsequently fitted with two peaks. One arises from the presence of oxygen atoms in the Te-O-Te, Mo-O-Mo and Te-O-Mo environments which are termed bridging oxygen (BO) and the other from oxygen atoms in an Mo@O environment which are termed non-bridging oxygen (NBO). The O 1s peak for x = 0.40 is more narrow and symmetric, and is fitted to a single peak due to the BO atoms. While the analysis of the Mo 3d spectra indicates the presence of Mo 6+ ions only, the temperature-dependent magnetic susceptibility measurements shows a weak paramagnetic behavior which can be explained by having less than 1 at.% of the Mo ions existing in a magnetic Mo 5+ valence state, a percentage below the detection level of the XPS determinations.