Ultrafast optical response of photoexcited states is studied by femtosecond pump and probe spectroscopy in a quasi-one-dimensional halogen-bridged mixed-valence platinum complex, [Pt(en)(2)][Pt(en)(2)Br-2](ClO4)(4) (en=ethylenediamine). We observed two kinds of photo-induced absorption (PA) signals, and both of the PA signal intensities follow non-exponential decay profiles. The signals are ascribed to two kinds of neutral soliton pairs with different configurations, that is, a spatially confined soliton and antisoliton pair and a noncorrelated soliton and antisoliton pair. Their formations are found to be closely related with both the excitation energy and the excitation density. (C) 2001 American Institute of Physics.