Functionalized multi-walled carbon nanotubes (f-MWCNT) with open ends, small diameters and functional groups at defect sites along their sidewalls were obtained by simple acid oxidation of pristine MWCNTs. The carboxylic acid functionalization of MWCNTs was confirmed using FTIR spectroscopy. f-MWCNTs show a considerably higher BET surface area with respect to pristine MWCNTs. Mebeverine Hydrochloride (MV.HCl) was determined based on functionalized multi-wall carbon nanotubes modified carbon paste electrode (f-MWCNT/CPE) as a sensor. The electrochemical properties of the modified CPEs were characterized using electrochemical impedance spectra (EIS), scan electron microscopy (SEM), and cyclic voltammetry. The modified electrode exhibited higher electrocatalytic activities toward determination of MV.HCl. f-MWCNTs lead to enrichment the electrode surface properties and decreases the charge transfer resistances of the modified electrode facilitating the electron transfer process. The modified electrode was successfully applied for trace determination of MV.HCl in different pharmaceutical preparations; "Coloverin A", "Colona" and "Colofac" tablets without interferences from excipients and co-formulated drugs. The achieved detection limit in human serum was 2.0 x 10(-10) M. The described adsorptive anodic stripping voltammetric method is reliable, simple and sensitive enough for assay of MV.HCl in real plasma samples, pharmacokinetic studies, quality control and assurance of the drug in industry and in clinical laboratories. (C) 2017 The Electrochemical Society. All rights reserved.