The reaction of Tc(+7) with H2O2 has been studied in HNO3 and the speciation of technetium was performed by UV/Vis spectroscopic analysis. UV/Vis measurements show that for HNO3 concentrations of more than 7 M and H2O2 concentrations of 4.25 M, Tc(+7) reacts immediately and red solutions are obtained, whereas no reaction occurs at H2O2 concentrations of 0.1 M. The UV/Vis spectra of the red solutions exhibit a single band centered at 500 nm that is attributed to a Tc(+7) peroxo species. The nature of the Tc(+7) peroxo species was investigated by computational methods. The structures and electronic spectra of the putative species Tc(O2)4–, TcO(O2)3–, TcO3(O2)–, TcO(O2)2(H2O)(OH), and TcO2(O2)(H2O)2(OH) were studied by first principles methods. Calculations show these species to be stable; their calculated spectra were compared to the experimental spectrum and the results are consistent with the presence of diperoxo pertechnetic acid, i.e., TcO(O2)2(H2O)(OH).