A study of the electronic structure and chemical bonding of the Li and proton exchange in spinel-type manganese oxides is performed by a first-principles molecular-orbital method using model clusters composing of 57 atoms. The discrete-variational (DV)-X alpha method was employed and Mulliken's population analyses were thoroughly conducted. We found that Li and proton in manganese oxides is highly ionized. Strong covalent interactions between Mn and O can be noted.