Abstract: V2O5 and MoO3 oxides are known as network formers and on this basis a series of two- and multicomponent non-conventional glasses have been synthesized. The structure of V2O5-MoO3–Bi2O3–Fe2O3 glasses was examined using IR and Mössbauer spectral investigations. Analysis of the spectra shows that in the V2O5 (MoO3)-rich region the main structural units forming the amorphous network are VO5(MoO6) groups connected by V-O-V (Mo-O-Mo)bridge bonds. Introduction of small amounts of Bi2O3 and Fe2O3 causes rapid transformation of the VO5 to VO4 (MoO6 to MoO4) groups (bands at 840–760 cm-1), and they become determining in a wide concentration range. According to the theory of Zachariasen, the existence of tetrahedral complexes connected by strong bridge bonds is necessary for the glass formation. In this case the VO4 (MoO4) groups are surrounded by MeO6 (Me = Fe, Bi) complexes which have longer bonds (their vibration frequencies being below 650 cm-1). They probably play the role of modifying units, break the V-O-V (Mo-O-Mo) bridge bonds and form Me-long Oshort-V (Mo) bonds. Thus, depolymerization of the vanadate and molybdate is achieved, which deteriorates the glass formation ability.