Thiolated chitosan (CS-TGA) was prepared using chitosan (CS) and thioglycolic acid (TGA). Then MWCNTs were added to the mixture of CS-TGA and CS to prepare the CS/CS-TGA/MWCNs porous composite by freeze-drying method and this composite was used to modify an indium tin oxide glass electrode. The electrode was used as a sensor for Pb2+. The morphology and structure of the composite were characterized by infrared spectroscopy and scanning electron microscope, and their electrochemical behavior was also studied. Under the optimized experimental conditions, the sensor showed a linear range of 2.0 x 10(-9) similar to 2.0 x 10(-8) mol L-1 for Pb2+ with a detection limit of 9.53 x 10(10) mol L-1 according to the 3 sigma rule. The prepared heavy ion sensor displayed excellent electrochemical response and high sensitivity.