Monodispersed gold nanoparticles (AuNPs) were prepared on glassy carbon electrode by multiple galvanostatic pulse strategy in the absence of any template or additional chemicals. The cyclic  voltammetry, differential pulse voltammetry, electrochemicalimpedance spectroscopyexperiments and quantum mechanical calculations were performed to unravel the mechanism of electrocatalytic reduction of uranyl (U^VIO₂²⁺) by AuNPs. The higher density of states of 5d band of gold nanoparticles and its strong interaction with the LUMO(U-5f) of [U^VIO₂(ƞ¹-OSO₃)( ƞ²-O₂SO₂), 2H₂O]^2-was found to be the most probable reason for catalyzing the heterogeneous electron transfer reaction. This is the first report on the participation of the 5f-orbital of actinyl ion in the electrocatalysis at AuNPs.