Laser flash photolysis of aqueous solutions of tris(2,2'-bipyridyl) ruthenium(II) cation (Ru(bpy)(3)(2+), bpy=2,2'-bi-pyridyl) induced transient absorbance changes in the near-IR region. The transient absorption with a peak at around 900 nm was assigned as a triplet-triplet transition of the metal-to-ligand charge transfer (MLCT) excited state of Ru(bpy)(3)(2+). The quantum efficiency for the MLCT state formation (phi) and the molar absorption coefficient at 900 nm (epsilon*) were determined to be phi = 1.00 +/- 0.04 and epsilon* = 1420 +/- 30 M-1 cm(-1), respectively, by applying the method of intensity dependence measurement.