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We report the temperature dependence of M6ssbauer spectra of a mixed-valence dinuclear Fe(II) Fe(IlI) complex, [Fe2(bpmp)(Ph(CH2)2COO-)2](BF4)2 1, where Hbpmp represents 2,6-bislbis(2-pyridylmethyl)aminomethyl]-4-methylphenol. Two quadrupole doublets observed at 78 K approach each other as the temperature is increased. The two high-energy components of a doublet due to Fe(II) and of that due to Fe(III) become broad in the temperature range from 78 to 230 K and then become narrow above 260 K. The temperature dependence of the spectra was interpreted by assuming of intramolecular electron exchanges between two energetically inequivalent vibronic states FeA(II)Fen(llI) and FeA(IlI)Fer~(lI) where one of them is slightly more stable than the other.