An ultrasensitive voltammetric sensor based on the synergistic effect of graphene (Grp)-Polyaniline (Pani) hybrid film for electrochemical sensing of antiprotozoal nitazoxanide has been developed. The electrocatalytic performance and morphology of fabricated hybrid film sensor were characterized by square wave voltammetry (SWV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The influence of various parameters such as pH, effect of scan rate, and loading of Pani-Grp hybrid film onto GCE on electroanalytical performance of the developed sensor was investigated. Under optimized conditions, reduction peak current was linear over the wide concentration range from 10-70 μg/mL with correlation coefficient of 0.998. The lower limit of detection (LOD) and the lower limit of quantification (LOQ) were found to be 2.2 μg/mL and 6.9 μg/mL. A novel electrocatalytic activity and the influence of hybrid film results in good characteristics such as high electroactive surface area, excellent electrochemical performance, anti-interferent ability, good stability, fast response, good reproducibility and long-term stability which are the promising features of the biosensing applications.Intrinsically conducting polymers, such as polyaniline (Pani), polypyrrole (PPY) and polythiophene (PT), have received considerable interest due to their fascinating electrical, optical and electrochemical properties derived from the conjugated p-electron system. 1 Composites of conducting polymers permit a facile flow of electronic charges across the polymer matrix during electrochemical processes. Polymer nanocomposite materials are important due to their extraordinary properties, which arise from the synergism between the properties of the components. 2-5 Among them, Pani shows the most promising material for electrical applications due to the existence of various oxidation structures (doped state) as well as due to their easy synthesis, good processibilty, high electrical conductivity, good chemical, thermal stability and environmental stability. 6-8 Pani shows attractive properties for use in chemical sensor and bio-sensors. 9,10 Pani has high specific surface area which would provide high sensitivity and fast response. 11 Graphene have extraordinary electronic transport properties and high electrocatalytic activities. 12-14 Graphene have been investigated as electrode materials in optoelectronic devices, electrochemical super-capacitors, fabricated field-effect transistors, and constructed ultrasensitive chemical sensors, such as pH sensors, gas sensors, and biosensors. 15 Graphene has become a material of choice in various research fields due to its characteristics of high electrical conductivity and large surface area. 16 Recently, graphene based materials have been used as an advanced nano electro catalyst for fabrication of electrochemical sensors. [17][18][19] The combination of the Grp with Pani highly enhances the electrochemical performance because Grp serves as a supporting material and provides a l...