The electronic state of M-2(WO4)(3) trivalent ion conductors (M = Al, Sc, Lu, Yb, Tm, Er, Y) was calculated by the discrete-variational X alpha molecular orbital (DV-X alpha MO) method. The bond overlap populations between the M3+ ion and the surrounding oxide ions and the net charge of M3+, W6+, and O2-ions were compared with the experimental ionic conductivity of M-2(WO4)(3) crystals. The variation of the activation energy of ionic conductivity agreed qualitatively with the change of the bond overlap population between the migrating trivalent ion and the surrounding oxide ions. This result suggests that the bonding state of the trivalent ions plays an important role in trivalent ion conduction in M-2(WO4)(3) crystals.