In this work, electrochemiluminescence resonance energy transfer (ECRET) between CdSe/ZnS quantum dot (QD) as the donor and cyanine dye (Cy5) as the acceptor in the conjugates consisting of QD, DNA and Cy5 was studied in detail. When a negative potential was applied to the conjugates immobilized on an Au electrode, QDs emitted a light with a maximum emission (lambda(m)) of 590 nm or transfered energy to proximal ground-state Cy5 molecules in 0.1 mol/L phosphate buffer (pH 7.4) containing 0.1 mol/L K2S2O8 and 0.1 mol/L KNO3. The excited state Cy5 molecules relaxed to their ground state by emitting a light with a lambda(m) of 675 nm. ECRET between QD and Cy5 in the conjugates could be used to evaluate the interactions between DNAs and to measure the conformational changes of DNAs as well as the distances between groups in DNAs. For the ECRET system, ECRET efficiency was high due to high Cy5-to-QD ratio and low Forster distance. (C) 2012 Published by Elsevier Ltd.