A carbon paste electrode modified with Sodium montmorillonite nanoclay (SMMT) was prepared and used for study and low level determination of D-penicillamine (D-Pen) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Compared with the unmodified carbon paste electrode, the modified electrode facilitated the electron transfer of D-Pen, since it notably increased the oxidation peak current of drug. The electronic transfer property of the SMMT carbon paste electrode was characterized by electrochemical impedance spectroscopy (EIS). Also, morphology of the electrode was characterized by scanning electron microscopy (SEM). Under optimized conditions, the modified electrode exhibited a linear response over the concentration range of 1-1000 mu M D-Pen, with a detection limit of 0.3 mu M. The proposed sensor exhibited a high sensitivity, good selectivity and was successfully applied for D-Pen determination in a D-Pen capsule. (C) 2014 Published by Elsevier B.V.