Eu(Ⅲ) can be utilized as an indirect electrochemical probe to investigate the interaction of bio-molecules such as DOPA and Dopamine with Ca(Ⅱ) in vitro. The interaction of DOPA and Dopamine with Eu(Ⅲ)-Eu(Ⅱ) redox pair was investigated by electrochemical techniques. Both the neurotransmitters are structurally related and undergo interaction with Eu(Ⅲ). Eu(Ⅲ) coordinates with DOPA and Dopamine through five-member chelate rings via carboxylic oxygen and amino nitrogen. The electrode kinetic parameters viz, transfer coefficient (α_ na ), diffusion coefficient (D), forward heterogeneous rate constant (k~0_ fh ) were evaluated for Eu(Ⅲ)-DOPA/Eu(Ⅲ)-Dopamine. The results obtained were used to investigate the nature of interaction of Eu(Ⅲ) with multi-donor biomolecules. The possible mechanism was also proposed. [BT(4+1] Eu (Ⅲ) can be utilized as an indirect electrochemical probe to investigate the interaction of bio-molecules such as DOPA and Dopamine with Ca (Ⅱ) in vitro. The interaction of DOPA and Dopamine with Eu (Ⅲ) -Eu (Ⅱ) redox pair was investigated by electrochemical techniques. Both the neurotransmitters are structurally related and undergo interaction with Eu (Ⅲ). Eu (Ⅲ) coordinates with DOPA and Dopamine through five-member chelate rings via carboxylic oxygen and amino nitrogen. The electrode kinetic parameters viz, The transfer coefficient (α_ na), diffusion coefficient (D), forward heterogeneous rate constant (k~0_ fh) were evaluated as Eu (Ⅲ) -DOPA / Eu (Ⅲ) -Dopamine. The results obtained were used to investigate the nature of Interaction of Eu (III) with multi-donor biomolecules. The possible mechanism was also proposed. [BT (4 + 1]