Pulse radiolysis studies of VK 1 were carried out in a nitrogen-saturated aqueous-isopropanol-acetone mixed solvent. We studied the spectroscopic characteristics of semiquinone radicals of VK 1 and determined the kinetic parameters of formation and decay of the species. It was found that the decay process of semiquinone radicals of VK 1 was according to a first-order reaction, this was different from the case in ethanol solution, possible reasons were also analyzed.