Nowadays, breast cancer is one of the riskiest and common cancer types. The early diagnosis of breast cancer is very important just as in other cancer types. Recent investigations demonstrate the biomarkers can be useful for the disease phase. These biomarkers are the very important materials to determine the good or bad diagnostic of the patient. Vascular endothelial growth factor is considered the most powerful mitogen for endothelial cells and also is an important regulator of vascular permeability and angiogenesis. In the frame of this study, it is purposed to design an electrochemical immunosensor system based on indium-tin oxide covered polyethylene terephthalate electrode. Electrochemical impedance spectroscopy, which is a quick and sensitive method, was used for vascular endothelial growth factor determination. Electrochemical impedance spectroscopy and cyclic voltammetry techniques were used in all optimisation processes of the produced biosensor. Scanning electron microscopy images, energy-dispersive X-ray spectra and mapping, atomic force microscopy and infrared spectra were examined to support the optimisation studies and to reveal surface morphology and chemical components. In the electrochemical characterisation studies, repeatability, reproducibility, storage, regeneration, single frequency impedance, square wave voltammetry and Kramer's-Kronig transform studies were performed. The measurements were taken in human serum.