Platinum nanoparticles (Pt-nano) were prepared and used in combination with single-wall carbon nanotube (SWNT) for fabricating electrochemical sensors with remarkably improved sensitivity toward diethylstilbestrol ( DES). The glassy carbon (GC) electrode modified with SWNT/Pt-nano composite film exhibited excellent electrochemical behaviors toward the redox of DES. Compared with the bare GC electrode and SWNTs film modified GC electrode, the redox peak currents at the SWNTs/Pt-nano composite film modified GC electrode was enhanced greatly. The experimental parameters, which influence the peak current of DES, were optimized. Under optimal conditions, a linear response of DES was obtained in the range from 1.0 x 10(-7) to 2.0 x 10(-5) mol L-1 (R = 0.997) and with a limit of detect (LOD) of 1.5 x 10(-8) mol L-1. The proposed procedure was successfully applied to determine the active ingredient in the DES tablet with satisfactory results.