The redox behavior, the molecular mechanism and electronic transfer of hydroquinone interacted with two forms Of L-Proline, covalent-linked to glass carbon electrode surface through C-N bond by electrooxidation and free dissolved in solution, were investigated by means of UV-vis and electrochemistry. The UV-vis spectrum showed that the reaction between free L-Proline and hydroquinone did not involve strong chemical bond. However, the electrochemical behavior of covalent-linked L-Proline is different from that of free one. Owing to electrostatic effect, the form of covalent-linked L-Proline favors electron transfer and enhances the reversibility of redox for hydroquinone. This phenomenon is conformed by cyclic voltammogram with a significant increase in peak current of hydroquinone redox and rate constant of electron transfer. It was found that it is a three-electron-transfer reaction. On the contrary, the form of free L-Proline unfavors electron transfer, resulting in a decrease in peak current of hydroquinone and rate constant, and the hydrogen bond was formed in the interaction. (c) 2006 Elsevier B.V. All rights reserved.