Using density functional theory calculations, we have investigated the interlayer cation exchange phenomena in muscovite mica, which is motivated by a necessity to develop flexible high-insulating covering materials. The crystalline structures, chemical bonding properties, energetics, and electronic properties of muscovites before and after exchange of interlayer K+ cation with ammonium (NH) or methylammonium (CH3NH) ion were calculated. It was found that the unit cell volume changes are negligibly small upon exchange with NH ion, while the unit cells are expanded with about 4 % relative rate when replacing the interlayer K+ cation with CH3NH ion. The energy band gap of pre-exchanged muscovite was calculated to be about 5 eV, which hardly changes upon interlayer cation exchange with either NH or CH3NH ion, indicating the preservation of high insulating property of muscovite. The exchange energies were found to be about -100 kJ/mol for NH and about -50 kJ/mol for CH3NH exchange, indicating that the exchange reactions are exothermic. A detailed analysis of atomic resolved density of states and electron density redistribution was provided.