An amperometric sensor for the determination of indole-3-acetic acid based on the multi-wall carbon nanotubes film coated glassy carbon electrode was developed. Multi-wall carbon nanotubes (MWNT) has been dispersed into water in the presence of hydrophobic surfactant such as dihexadecyl hydrogen phosphate (DHP). The indole-3-acetic acid sensor was achieved via evaporating solvent of the MWNT-DHP dispersion on the GCE surface. The oxidation peak current of indole-3-acetic acid (IAA) increases significantly at the MWNT-DHP film coated GCE, in contrast to that at the bare and the DHP-coated GCE, and the oxidation peak potential is at 0.68 V (versus SCE), which can be used for the detection of IAA. The electrochemical behaviors of IAA at the MWNT-DHP modified GCE have been examined by cyclic voltammetry. The experimental parameters were optimized and an electrochemical method for the determination of IAA was established. The oxidation peak current is linearly with the concentration of IAA from 1 Γ 10 -7 to 5 Γ 10 -5 mol/l and the detection limit is 2 Γ 10 -8 mol/l. The relative standard deviation of eight measurements is 3.6% for 5 Γ 10 -6 mol/l IAA. The IAA in plant leaves were extracted and determined by the IAA sensor.