Heavy metal ion pollution has threatened environmental and human safety. Therefore, there is a remarkable demand to detect heavy metal ions in a fast, sensitive, and selective way. Although conventional sensors have been designed and widely applied in heavy metal ion determination, they present many limitations and challenges. Graphene-based nanotechnology overcomes these challenges and endows the sensing platform a better performance. In this overview, studies concerning graphene-based optical nanosensors for heavy metal ion detection have been summarized, paying special attention to sensors based on graphene, graphene oxide, and graphene quantum dots. In addition, the prospects and developing trends of nanosensors for heavy metal ion analysis are also proposed. •Graphene-based hybridized nanocomposites for metal ion optical detection were reviewed.•Graphene or GO as fluorescence probes for heavy metal ion detection was summarized.•Graphene or GO as the fluorescence quencher for heavy metal ion analysis was described.•Applications of GQD and CD probes in heavy metal ion sensing were discussed.