This work describes the modification of a glassy carbon electrode with poly(Toluidine Blue O) (GC/poly-TBO) and single-walled carbon nanotubes (SWCNT) for the electrocatalytic oxidation of nitrite. GC/poly-TBO was prepared by electropolymerization and used as such or after immobilizing SWCNT on the polymeric film to give a composite GC/poly-TBO-SWCNT electrode. The electrochemical and catalytic behavior of both electrodes was studied comparatively. It was observed that the presence of SWCNT contributed to enhance the electrocatalytic response for nitrite oxidation, as measured by amperometry at +0.92 V vs. Ag/AgCl/KClsat and pH 7. The response was linear with respect to the nitrite concentration in the 0.001-4 mM range, with a detection limit of 0.37 mu M (based on signal to noise ratio of 3) for GC/poly-TBO-SWCNT. The proposed method was also applied to the determination of nitrite in a wastewater sample and compared to the spectrophotometric method.