A carbon nanotube/Nafion composite film modified electrode is described for the sensitive and convenient determination of Pb2+. In the presence of 1% Nafion, multi-walled carbon nanotubes (MWNT) were successfully dispersed into ethanol by ultrasonication. After evaporating the ethanol, a MWNT/Nafion composite film-modified electrode was achieved. The resulting MWNT/Nafion film modified electrode possesses high cation exchange capacity, large surface area, strong adsorption ability and catalytic activity. Compared with the unmodified electrode and Nafion film-modified electrode, the MWNT/Nafion film-modified electrode remarkably increases the stripping peak current of Pb2+. Furthermore, the influences of supporting electrolyte, volume of MWNT/Nafion suspension, accumulation potential and accumulation time were investigated. The striping peak current of Pb2+ is proportional to its concentration over the range 8.0 x 10(-8) to 6.0 x 10(-6) mol L-1. The limit of detection (S/N = 3) is as low as 5.0 x 10(-9) mol L-1. Finally, this newly developed method was used to determine Pb2+ in water samples.