Gold nanostructures (GNs) modified electrode, which was fabricated by simple, cost-effective one-step electrochemical technique, was used for the development of an electrochemical immunosensor for the detection of CA125 antigen. The morphology of the GNs modified electrodes was easily controlled by changing the pH of the source gold electrolyte and the electrodeposition time. The GNs electrode has shown excellent electrochemical performance compared with flat bare Au electrode. Hence, the GNs electrode was used for the fabrication electrochemical immunosensor. The immobilization and sensing properties of the GNs modified bioelectrode is characterized by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry with Fe(CN)(6)(3-/4-) as an electrochemical redox indicator. The developed GNs based electrochemical immunosensor offers good response for the detection of CM 25 antigen with a linear range (10-100 U mL(-1)), low detection limit (5.5 UmL(-1)). Thus, the fabricated immunosensor have potential applications as an enhance biosensing platform for biomolecules immobilization and detection. (C) 2016 Elsevier B.V. All rights reserved.