An in situ modified Hummers method (without the use of any surfactants) has been used for the deposition of bismuth (Bi) nanoparticles onto the surface of reduced graphene oxide (RGO) sheets. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), thermogravimetry (TG) and differential scanning calorimetry (DSC). The morphology of the RGO/Bi nanocomposites provides a better choice as an electrode material for detection of heavy metal ions due to its better functional properties over the Bi film electrode. Trace analysis of heavy metal ions like Cd+2, Pb+2, Cu+2 and Zn+2 in water is carried out by stripping voltammetric analysis using RGO/Bi nanocomposite as an electrode material. The sensitivity and detection limit of the electrode were quantitatively estimated from the analysis. The three sigma detection limits at different deposition potential for Cd2+, Pb2+, Zn2+ and Cu2+ were obtained as 2.8, 0.55, 17 and 26μgL−1, respectively. Copper detection using Bi-film electrode was a major challenge, which has been resolved using the RGO/Bi nanocomposite electrode. ► RGO/Bi nanocomposite synthesized by modified Hummers method without surfactant. ► Reduction of GO and formation of Bi nanoparticles are accomplished simultaneously. ► Trace analysis of heavy ions with composite as electrode by stripping voltammetry. ► Detection limit for Cd2+, Pb2+, Zn2+, Cu2+ were 2.8, 0.55, 17 and 26μgL−1. ► Copper detection using Bi-film electrode resolved using these composites.