The improper disposal in agricultural and industrial wastewater leads to high NO2- concentrations in the aquatic environment, which can cause cancer in humans and animals; thus, their quick and accurate detection is urgently needed to ensure public health and environmental safety. In this study, a reliable and selective electrochemical sensor consisting of Pd-Cu nanospheres (NSs) supported on molybdenum carbide was prepared via simple ultrasonication. Then, a glassy carbon electrode was realized using this composite (Pd-Cu-Mo2C-modified GCE) to test its electrocatalytic sensing for NO2- in a 0.1 M phosphate-buffered solution (PBS) solution via cyclic voltammetry and amperometry; at a low oxidation potential, the anodic peak current of NO2- detected by this electrode was significantly higher than that of its unmodified and other modified electrodes. The sensor showed a broad linear response in the 5-165-nM NO2- concentration range, with a low detection limit (0.35 nM in 0.1 M PBS) and high sensitivity (3.308 μAnM-1 cm-2). Moreover, the fabricated electrode was successfully applied for detecting nitrites in sausages, river water, and milk, showing also good recovery.