In this work, an electrochemical sensor based on a Fe₃O₄/STAB/chitosan nanocomposite was developed for the detection of nitrite. The nanocomposite exhibited positive charges on its surface, high conductivity, favorable biocompatibility, and strong antifouling ability, enabling electrostatic adsorption of nitrite and thereby enhancing detection sensitivity. A glassy carbon electrode (GCE) modified with this material was employed for nitrite measurement using differential pulse voltammetry (DPV). Under optimized conditions, the Fe₃O₄/STAB/chitosan/GCE showed excellent analytical performance for nitrite detection, with a detection limit of 0.151 mg/L. Recovery rates of nitrite in real samples ranged from 95.02% to 107.93%, with relative standard deviations between 0.91% and 5.23%. Moreover, the modified GCE displayed excellent selectivity, reproducibility, and repeatability for nitrite detection. Therefore, this work provides a novel strategy for nitrite monitoring in aquaculture.