•Novel Sn doped Zinc oxide hexagonal micro discs anchored are on rGO.•Lattice constant parameters of Wurtzite hexagonal ZnO structures is analyzed.•Sn-ZnO/rGO/GCE exhibited an ultra-low LOD of 7.3 nM to linear range 0.01–170 µM.•The sensitivity of the sensor is 14.10 µA µM−1 cm−2 towards flutamide (FLU).•Real-time monitoring is carried out in river and biological samples. Prostate cancer is one of the major causes of death around the globe leading to cancer deaths in the US standing at a second position. Flutamide is one of the important drugs which is utilized in clinical diagnosis. Even though over usage and improper discharge leads to very serious harm to both living and environmental bodies. In this aspect developing a sensor for ultra-trace level detection of flutamide is very much indeed with selectivity, stability, and reproducibility. Herein, we report a facile synthesis of hexagonal Sn doped zinc oxide (Sn-ZnO) anchored on reduced graphene oxide (rGO) hybrid nanocomposite in discriminating reduction of flutamide. As per prepared Sn-ZnO/rGO nanocomposite has exhibited good catalytic performance when compared to bare and other modified electrodes. Resulting in inactive sites, large surface areas, synergic effects, and crystalline growths. Noticeable merits include the wide linear range of 0.01 to 170 µM and Limit of detection (LOD) of 7.3 nM with an excellent sensitivity of 14.10 µA µM−1 cm−2 and satisfying stability. The modified electrode was successfully applied as a real-time analysis in both biological and water bodies with promising recoveries.