A series of V2-xMoxO5 (x equals 0.2, 0.4, 0.6, 0.8) samples has been investigated by X-ray photoelectron spectroscopy (XPS). MoO3, VO2, V2O5 (powders), VO2(c) and Na0.33V2O5(c) have been used as reference samples. According to the XPS measurements, the valence of Mo atoms in this series is not changed during the Mo doping and it is close to that of MoO3. The V atoms show a mixed valence in the V2-xMoxO5 system: with increasing of the Mo content, a higher concentration of tetravalent V atoms is observed. For one sample of this series, V1.2Mo0.8O5, it was found that the XPS valence band and also the core level spectra are close to those of another mixed- valence system, Na0.33V2O5. Both compounds show similar electrical properties, which can be interpreted in terms of a two-level hopping model. It is concluded that the impurity states in the band gap of both compounds have 3d like character and they are formed at the expense of the additional electrons of Mo or Na.