Abstract: Glassy carbon electrode (GCE) was modified by dropping a suspension of graphene oxide (GO), multi-walled carbon nanotubes (MWNTs) and carboxymethyl chitosan (CMCS) onto its surface to obtain the modified electrode of MWNTs/GO/CMCS/GCE. Electrochemical behaviors of NO₂^- and L-tryptophan (L-Trp) at the modified electrode were studied by cyclic voltammetry (CV). The effective area of the modified electrode was found to be 3.243 0×10^-6cm², which was significantly increased as compared with the bare electrode and thus electron transfer was accelerated and adsorption-enrichment of the analytes was facilitated. As shown by the results, significant electro-catalytic oxidations of NO₂^- (in PBS of pH 4.7) and L-Trp (in acetate buffer of pH 4.0) were observed at the modified electrode separately, and linear relationships between values of the oxidation peak current and the concentration of NO₂^- in the range of 1.0×10^-7 to 3.5×10^-1mol·L^-1 and of L-Trp in the range of 1.0×10^-8 to 2.7×10^-1mol·L^-1 were obtained, with detection limits (3S/N) of 1.2×10^-8mol·L^-1, and 5.0×10^-8mol·L^-1 respectively. NO₂^- in a sample of rotten cos lettuce and L-Trp in a simulated sample were determined by the proposed CV method, giving results in consistency with those found by UV-spectrophotometry (for NO₂^-) and by fluorospectrophotometry (for L-Trp).