Abstract: Solid paraffin lidocaine modified carbon paste electrode based on the complex of HgI42- with lidocaine as electroactive material was prepared and its electrochemical properties were studied. Good response of this ion selective electrode against lidocaine was obtained giving linearity range from 5.0×10-5 to 1.6×10-2mol·L-1, with a slope of 29 mV/pc and lower limit of determination of 1.3×10-5mol·L-1. The modified electrode was used in the potentiometric determination of lidocaine in lidocaine injection, and results obtained were found to be checked quite well with those found by the pharmacopoeia method.