Chemical bonding character of the glass network forming M-O bonds (M = Si, B, Ge, and Al) was evaluated based on the Mulliken population analyses, in which the bond overlap population QMO was obtained from the molecular orbital calculations. It was found in alkali silicates that the interaction of alkali ion with bridging oxygen reduced Qsio in Si-O-Si bridging bonds, and Qsio in Si-O-Na terminal bonds was much larger than that in Si-O-Si bridges. In M-O-M bridges, that is, Si-O-Si, B3-O-B3, B4-O-B4, Ge4-O-Ge4 (Bn, Gen: n-fold coordinated boron and germanium), QMO was distributed around 0.6 ± 0.I. In M-O-M′ bridges formed by the heterogeneous combinations of B3-O-B4, Ge4-O-Ge5, Ge4-O-Ge6, Si-O-B4, and Si-O-A14, QMO of M-O bond was larger than QM′O of M′-O bond, and the difference between QMO and QMO was about 0.2. It was suggested that the dispropoitional sharing of electrons reflected the π-bonding character, that is, more electrons were localized on the bonds with larger it-bonding character.