Transient species (T1and T2), formed respectively by the reactions of hydrated electrons and hydroxyl radicals with methyl vinyl ketone monomer in aqueous solution, were characterized by their spectra, redox behavior, and decay kinetics. These were found to have λmaxat 290 and 310 nm with low extinction coefficient values of 94 and 70 m2/mol, respectively. Rate constants for the reactions of methyl vinyl ketone with eaaq- and OH were found to be 3.2 × 109 and 7 × 108 dm3·mol−1·s−1, respectively. the first propagation step for species T2 was found to be much faster (κpl∼ 1.5 × 106 dm3·s−1than that for species T1(κpl∼7.0 × 105 dm3·mol−1·s−1). Both were found to be reducing in nature, and the rate constants for the reduction of thionine and safranine with these species were determined. the most probable structures of these species are suggested.