Dissolution of Uranium oxides and their redox speciation in two imidazolium-based DES. • New DES based on imidazolium cation are studied for the uranium oxide dissolution. • Redox speciation of UO 3 and UO 2 in imidazolium-based DES was thoroughly probed. • Interestingly, Uranyl species formed in the case of UO 3 but not in the case of UO 2 . • Theoretical simulations adequately validated the experimental results. Two new deep eutectic solvents, different from hitherto known and based on common choline chloride, were prepared. 1-methyl-3-decylimidazolium bromide mixed with hydrogen bond donors, malonic acid and diglycolic acid to form DES. Dissolution of uranium oxides (UO 3 and UO 2 ) was explored in both of them and characterization of the resultant solutions was carried out by IR, TGA and UV–Vis spectroscopy. Redox speciation of dissolved uranium oxides was probed in these redox-active DES through cyclic voltammetry, differential pulse voltammetry and in situ spectroelectrochemical measurements. Interestingly, the formation of uranium oxo species was observed through the dissolution of UO 3 in both the DES. The electrochemical characteristics viz. redox thermodynamics (peak potential and formal redox potential), transport property (diffusion coefficient D 0 ), heterogeneous electron transfer kinetic parameters (αn and k 0 ) and mechanistic electron transfer of the dissolved uranium species in two DES were investigated. The speciation of uranium was decoded through the electronic absorption spectra of uranium in its lower oxidation states [U(V) and U(IV)] acquired through in situ spectroelectrochemical electrolysis with varying cathodic potentials. Studies were also carried out using Molecular Dynamics (MD) and density functional theory (DFT) simulations to authenticate the electrochemical outcomes and to acquire the binding energy, optimized structure and molecular orbital diagram of dissolved uranium species. Further, the MD simulation sheds light on the probable equatorial coordinating atoms of dissolved uranium species. This is the first report, to the best of our knowledge, on imidazolium-based DES and actinide ions.