The performance of isoquinoline, a kind of nondegradable ,N,-heterocyclic compound, under the irradiation of UV light and its reaction with HO∙ were investigated by pulse radiolysis and laser flash photolysis. It was shown that both photo-excitation and monophoto-ionization with the quantum yield of 1.58×10,-4, happened in isoquinoline under the irradiation of the laser pulse of 266nm. The cation radical of isoquinoline produced by photo-ionization could deprotonate to form its conjugate base mediate radical with the pKa of 5.50. Pulse radiolysis showed that isoquinoline could react with HO∙ very rapidly with the rate constant of 3.4×10,9, mol,-1,•dm,3,•s,-1,. With a better understanding on pulse radiolysis and laser flash photolysis of isoquinoline, this study is helpful for its degradation and for environment protection.