Driven by the academic interest, we have studied the aqueous electrochemistry of neptunium (Np) in 1 M nitric acid solution on the electrochemically reduced graphene oxide (ERGNO) modified glassy carbon (GC) electrode. Similar to our previous experiences on the electrocatalytic action of ERGNO on the electrochemistry of uranium(VI)/uranium(IV) and plutonium(IV)/plutonium(III) redox couples, the present study confirms the robust electrocatalytic ability of ERGNO for the redox reaction of (NpO22+)-O-(VI)/(NpO2+)-O-(V) in acidic solution even at high anodic working potentials. The extent of the electrochemical reversibility of (NpO22+)-O-(VI)/(NpO2+)-O-(V) redox couple increases on ERGNO compared to the bare GC electrode. For the first time, the electron transfer reaction of (NpO22+)-O-(VI)/(NpO2+)-O-(V) redox couple is investigated by electrochemical impedance spectroscopy. The improved sensitivity as well as the lower limit of detection of Np by anodic square wave voltammetry on ERGNO compared to bare GC opens up the application of ERGNO in the nuclear science and technology. (C) 2015 Elsevier Ltd. All rights reserved.