Electrochemical upgrading of carbon dioxide (CO2) into high-value chemicals and fuels provides a potential way to close the anthropogenic carbon cycle and store renewable energy. Heteroatoms (e.g., sulfur, nitrogen, boron, phosphorus, etc.) doped nanostructured carbon materials have been under development as a category of metal-free electrocatalysts for CO2/CO reduction due to their low cost, large specific surface area, and tunable electronic structure, and Cu is the only known metal catalyst that can convert CO2/CO to high-order hydrocarbons and oxygenates. However, little progress has been made in regulating Cu loading in heteroatoms doped nanostructured carbon materials for electrochemical CO2/CO reduction reaction (CO2/CORR). Herein, we report the effect of trace Cu loading in graphene quantum dots (GQDs) on CO2/CORR. Electrocatalytic measurements show a significant loading effect in both the activity and selectivity toward CO2/CORR. Increasing the Cu loading in GQDs will improve catalytic activity and selectivity toward C2 from C1 productions in CO2/CORR. The activity/selectivity relations provide a clean understanding of the synergistic effect of GQDs and trace Cu in CO2/CORR.