The electrochemistry of l-cysteine (CySH) in neutral aqueous media was investigated using carbon ionic liquid electrode (CILE). Comparative experiments were carried out using glassy carbon electrodes. At CILE, highly reproducible and well-defined cyclic voltammograms were obtained for l-cysteine with a peak potential of 0.49 V vs Ag/AgCl, showing that CILE manifests a good electrocatalytic activity toward oxidation of l-cysteine. A linear dynamic range of 2–210 μM with an experimental detection limit of 2 μM was obtained. The method was successfully applied to the determination of l-cysteine in a sample of soya milk. Cysteine oxidation at CILE does not result in deactivation of the electrode surface. Mechanistic studies showed that, at CILE, the overall CySH oxidation is controlled by the oxidation of the CyS − electroactive species.