In consideration of the imperious need for developing a simple, ultra-sensitive and selective method to detect Hepatitis B virus (HBV), an label free aptasensor was constructed by the modification of a chemically inert glassy carbon electrode (GCE) by dint of a gold nanoparticle immobilized reduced graphene oxide. The ultrasensitive detection was attained using a specific ssDNA (thiolated aptamer at the 5′ end) as a recognition element. The aptamer was fastened onto GCE/rGO/Au surface via the Au-S bond for determining the impedance of charge mobility by means of [Fe(CN)₆]^3-/4- as a redox gauge. The function of aptasensor based on the specific interaction between the aptamer and specific surface antigen HBsAg induced [HBsAg-aptamer] complex formation which impeded electron movability between a [Fe(CN)₆]^3-/4- redox probe solution and sensing interface. HBsAg-binding aptamer events can be easily monitored by the signal switch through cyclic voltammetry technique (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) measurements. Under the optimized conditions, the aptasensor can detect HBsAg in the 0.25 fg/mL to 1.5 fg/mL concentration range and limit of detection of 0.018, 0.0016 and 0.001 fg/mL for CV, SWV and EIS respectively. The recovery of 88-109.6% was obtained. Moreover, the selectivity of the aptasensor was tested using other biological interfering substances. This developed aptasensor provided one of the lowest limits of detection for HBsAg recently reported in the literature, satisfying stability and good reproducibility, consequently could be applied for revealing HBsAg in real samples.