We report the fabrication of a novel amperometric sensor for tryptophan (Trp) based on a pristine multi-walled carbon nanotube/graphene oxide (pMWCNT/GO) hybrid obtained through the sonication of pMWCNTs in an aqueous solution of GO. The results of transmission electron microscopy and electrochemical impedance spectroscopy demonstrate the successful formation and the excellent charge transfer ability of the resulting hybrid. Compared with the commonly used acid-treated MWCNTs and GO, the resulting hybrid exhibits better electrocatalytic activity towards the oxidation of Trp, which is attributed to the synergistic effect of MWCNTs and GO. The current–time curve reveals that the catalytic oxidation current is linearly dependent on Trp concentration in the range of 50 nM to 4.25 μM with a detection limit of 8 nM (S/N = 3). In addition, the proposed sensor is successfully employed to detect Trp in the real samples with satisfactory results.