The mechanism and electron transfer for pollutant dihydric phenol and biomolecule L-Cysteine (L-Cys) interaction in aqueous solution were studied by means of electrochemistry and UV-VIS spectrophotometry. Two forms of L-Cys, fixed on Au-electrode and free dissolved in the solution, were examined. The results showed that L-Cys of an ordered monolayer fixed on an Au electrode facilitated electron transfer and electrocatalytic redox of three isomers of dihydric phenol. However, free L-Cys does not show such facility. Furthermore, neither cleavage of the original chemical bond nor formation of a new chemical bond was observed in the molecules investigated, suggesting that L-Cys molecules may associate tightly with dihydric phenol molecules to form L-Cys . C(6)H(6)O(2)or (L-Cys) (2) . C(6)H(6)O(2) complex molecule via hydrogen-bonding. Different coordination numbers influence the electrochemical activity and behavior of associated complexes; thus, the function of biomolecules could be affected.