The poly (3,4-ethylenedioxythiophene) (PEDOT) nanomaterial was synthesised by a facile electrodeposition on a glassy carbon electrode (GCE) modified by carboxylated multi-wall carbon nanotubes (CA-MWCNTs). The nano-composite was characterized using transmission electron microscopy, scanning electron microscope, energy dispersive X-ray spectroscopy and fourier transform infrared spectroscopy. Moreover, a highly sensitive ascorbic acid (AA) sensor was developed based on the nanocomposite. Owing to the combination of the advantages of CA-MWCNTs and PEDOT, the modified electrode exhibited excellent electro-catalytic activity for AA detection which was investigated in detail by cyclic voltammetry and chronoamperometry. The cationic PEDOT film on CA-MWCNTs could interact with anionic AA in neutral PBS at a low potential and distinguish the oxidation peaks of common interfering species. The effects of electrodeposition time and pH value on the current responses of the modified electrode towards AA were optimized to obtain the maximal sensitivity. The prepared AA sensor demonstrated high sensitivity (1699.36 mu A mM(-1) cm(-2)), wide linear range detection (100 mu M to 20 mM), low detection limit (4.2 mu M), rapid response time (less than 4 s), good selectivity and long-term stability. This work presented a facile approach for future research in AA amperometric sensors. (C) 2016 Elsevier B.V. All rights reserved.