Copper (Cu) doped II–VI semiconductor quantum dots (QDs) manifest high luminescent dopant emission with excellent tunability. The Cu-doped II–VI QDs have been well studied via optical spectroscopy; nevertheless, the electrochemical study on doped QDs where the signals are traced to discover the absolute energies of dopant and band-edges of the host is rarely investigated. Herein, we have estimated these energies in 2 nm Cu-doped CdS QDs via cyclic voltammetry (CV). The CV graph of doped QDs revealed a specific intragap state where the redox potential is near to the Cu energy state. The observed results from the CV analysis were well correlated with optical spectra.