Transient absorption of 2-(2,4-dinitrobenzyl)pyridine (α-DNBP) has been measured by a nanosecond laser photolysis to elucidate the dynamical behavior of a photoinduced intramolecular proton transfer (PIPT). On UV light photolysis, α-DNBP changes from a colorless to a dark blue form. The dark blue form consists of the OH, OH−and NH forms whose absorption bands are located at ∼400, ∼490 and ∼570 nm, respectively. We found an additional absorption band located at 660 nm. From the observed transient behavior of the band, we assign this band to be the lowest absorption band of the OH form. The PIPT reaction pathways and their time constants of α-DNBP also have been determined.