An ordered mesoporous silica ( OMS ) was synthesized through hydrothermal process. The synthesized material was characterized by different techniques such as X-ray diffraction, nitrogen adsorption-desorption and transmission electron microscope. The electrochemical characteristics of the OMS modified carbon paste electrode ( OMS/CPE ) were investigated by using cyclic voltammetry and electrochemical impedance spectroscopy. Compared with bare carbon paste electrode ( CPE ) , the OMS/CPE exhibited a larger electrode surface and a faster electron-transfer rate. Electrochemical behaviors and kinetic properties of L-tryptophan ( L-Trp) at the OMS/CPE in the presence of sodium dodecylsulphate ( SDS) were studied. The results showed that the voltammetric response of L-Trp at OMS/CPE was improved due to the synergistic effect of OMS and SDS. The electrochemical oxidation of L-Trp at OMS/CPE in the presence of SDS was an irreversible process involved two electrons and two protons, and the electrode process was controlled by the adsorption step. Some parameters such as SDS concentration, accumulation time, accumulation potential and pH were optimized. Under optimal conditions, the oxidation peak current was linearly proportional to L-Trp concentration in the range of 8. 0×10-8 to 4. 0×10-6 mol/L, with a detection limit of 7. 0×10-8 mol/L (S/N=3 ) . The proposed method was applied for the determination of L-Trp in oral liquid with the recoveries of 99 . 6%-102 . 6%.