The fast and sensitive detection of copper ions would be essential for water monitoring. Herein, we report a novel development of an impedimetric sensor based on carbon dots/chitosan nanocomposite. Carbon dots (CDs) were synthesized by simple heating of an acidic aqueous solution of glucose. The prepared CDs were characterized by TEM, FTIR, XRD, UV-visible, and PL. These measurements revealed that the CDs possess a mean size of 3.2 nm, a graphitic structure with carboxyl and hydroxyl groups on the surface, and shows particular optical properties. A glassy carbon electrode (GCE) was modified with a carbon dot/chitosan nanocomposite and was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The CDs-CHITO/GCE electrode exhibits a large surface area, good conductivity film, and charge transfer at film/electrolyte interface. The proposed impedimetric sensor exhibits a linear response to Cu(II) ranging from 10−9 M to 10−5 M with a detection limit about 5 × 10−10 M. In addition, the sensor shows a good selectivity toward Cu(II) ions, which is less than 5%. Therefore, the as-developed impedimetric sensor exhibits good reproducibility, stability, selectivity, and a low limit of detection, which augur well for its application in water safety control processes.