Variable-temperature Mössbauer spectra were measured for biferrocenium+F4TCNQ−(2) and 1′,1′′′-diethylbiferrocenium+F4TCNQ−(3) in order to elucidate their mixed-valence states, where F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane. A valence-delocalization between Fe(II) and Fe(III) sites on elevating the temperature was observed for2; The Mössbauer spectra of2below 298 K consisted of two quadrupole doubets corresponding to the Fe(II) and Fe(III) atoms in2, and the spectrum at 320 K consisted of only one quadrupole doublet showing a single valence state of iron averaged over Fe(II) and Fe(III). On the other hand, compound3showed trapped-valence type spectra in the whole temperature range of 4.2 - 320 K.