Indirect competitive electrochemical immunosensor for hepatitis A virus antigen (HAV) detection was developed by immobilizing HAV on the surface of carbon nanopowder paste electrode. The monitoring of the target HAV antigen was performed using a secondary antibody labeled with peroxidase. The analytical signal corresponds to an amperometric current resulting from the addition of hydrogen peroxide and hydroquinone as a redox mediator. A calibration curve was obtained by plotting the intensity of the amperometric signal versus the concentrations of HAV antigens. A low detection limit for HAV antigen was attained and estimated to be 26.10(-5)IU.mL(-1). The sensitivity was also investigated and compared with indirect competitive ELISA. Moreover, the immunosensor provides exact results over a broad linear range from 2.10(-4) to 5.10(-3) IU.rnL(-1), (R-2 = 0.998). The average relative standard deviation (RSD) of this method was less than 3% for the assays performed on the same day and 7% for the measurements made on different days. The immunosensor exhibits a good stability and high biological selectivity for HAV antigen detection and was successfully applied for the determination of HAV in water samples.