The photochemical reaction of potassium ferrocyanide (K4Fe(CN)6}) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K4Fe(CN)6 were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and phtoaquation reactions were clarified by comparing the results of 260 , 320 , 340 , and 350 nm excitations. ESED is the path to generate a hydrated electron (eaq-). ESED energy barrier varies with the excited state, and it occurrs even at the first singlet excited state (1T1g). The 1T1g state shows ~0.2 ps lifetime and converts into triplet [Fe(CN)6]4- by intersystem crossing. Subsequently, 3[Fe(CN)5]3- appears after one CN- ligand is ejected. In sequence, H2O attacks [Fe(CN)5]3- to generate [Fe(CN)5H2O]3- with a time constant of approximately 20 ps. The 1T1g state and eaq- exhibit strong reducing power. The addition of UMP to the K4Fe(CN)6 solution decreased the yield of eaq- and reduced the lifetimes of the eaq- and 1T1g state. The obtained reaction rate constant of 1T1g state and UMP was 1.7×1014 M-1 s-1, and the eaq- attachment to UMP was ~8×109 M-1 s-1. Our results indicate that the reductive damage of K4Fe(CN)6 solution to nucleic acids under ultraviolet irradiation cannot be neglected.