A pair of well-defined redox waves of folic acid at a 2-mercaptobenzothiazole self-assembled gold electrode (MBT/SAM/Au) was achieved. Folic acid can bind strongly to MBT/SAM/Au and form a closely packed monolayer, whose average electron transfer rate is 0.085 s(-1) with a two-electron/two proton transfer, a maximum surface coverage of 2.8 x 10(-10) mol cm(-2), an adsorption equilibrium constant of (4.0 +/- 0.2) x 10(5) l mol(-1), and an electrode reaction resistance of 12489 Omega. The oxidation peak currents achieved on MBT/SAM/Au vary linearly with the logarithm of the content of folic acid in the range of 8.0 x 10(-9)-1.0 x 10(-6) mol l(-1). The detection limit is 4.0 x 10(-9) mol l(-1). This can be used to determine folic acid.