Herein, an electrochemical sensor was developed for detecting heavy metal ions by using a carboimidazole grafted reduced graphene oxide (reduced graphene oxide-NH-carboimidazole, abbreviated as RGO-NH-Ci) modified electrode. The morphology of RGO-NH-Ci material was characterized by scanning electron microscopy (SEM). The electrochemical behaviors of the RGO-NH-Ci modified electrode toward heavy metal ions, including Hg2+ and Pb2+, were investigated with differential pulse anodic stripping voltammetry (DPASV). Compared with pure reduced graphene oxide (RGO), RGO-NH-Ci modified electrode showed improved analytical performance in detecting the two metal ions owing to the strong complexing capacity of Ci and the presence of the amino groups. The detection limits were estimated to be 0.2 nM and 3.0 nM for Hg2+ and Pb2+, respectively, under the optimized conditions. The developed method was also employed to detect the Hg2+ and Pb2+ in real water samples, and satisfactory results were obtained. (C) 2016 Elsevier B.V. All rights reserved.