Au and Pt complexes form oligomers because of the metallophilic interaction. A mixed aqueous solution of [Pt(CN)4]2- and [Au(CN)2]- (Pt-Au aqueous solution) showed emission with a higher yield than pure Au or Pt aqueous solutions of the same concentration. Ultrafast time-resolved absorption spectroscopy was performed on the Pt-Auaqueous solution. Considerable oscillations of the time-resolved absorption signal with a frequency of around 60 cm-1 were observed at 370 and 400 nm. Because the frequency, monitoring wavelength, and magnitude of the oscillations differ from those observed in Au or Pt aqueous solutions, this vibration is assignable to that of an excited-state Au-Pt hetero- oligomer.