Changes in electronic structure upon electrochemical lithium insertion into two iron compounds, namely, rhombohedral Fe-2(SO4)(3) with a NASICON-type structure and monoclinic Fe-2(MoO4)(3), were investigated using X-ray absorption spectroscopy (XAS). Fe K-edge and L-III- and L-II-edge XAS revealed that the rearrangement of Fe d electrons or rehybridization of Fe d-O p bonding took place accompanied by the reduction of Fe ions upon Li insertion for both samples and that a larger change in spectra was observed in Fe-2(SO4)(3). In addition, the changes in the electronic structure of the polyanion units XO42- (X = S or Mo) after Li insertion were also investigated by O K-edge and S K-edge or Mo L-III-edge XAS. The results indicated that the electronic structure around oxygen markedly changed in Fe-2(MoO4)(3), while no significant change was observed in Fe-2(SO4)(3).