Electrochemiluminescence (ECL) is a powerful technique that combines the best features of electrochemistry and chemiluminescence in a single experiment. Its versatility, simplified optical set-up, low background signal and high sensitivity [1] allows the increase of new analytical applications. ECL signals are usually obtained from the excited states of a luminophore generated at the electrode surface during an electrochemical reaction due to the presence of a co-reactant. Particularly, resonance energy transfer (RET) mechanism is produced when at least two luminophores are present in solution, one luminophore acts as donor and the other one as acceptor [2]. In the absence of an external light source, donor luminophore emits light as consequence of its electrochemical excitation, part of this emission is absorbed by the acceptor to be excited and re-emits light.Initially, ECL emission of two luminophores were separately analysed in this work: (1) luminol emission in presence of hydrogen peroxide as co-reactant shows one band from 350 to 600 nm (maximum at 420 nm) during its oxidation process at +0.20 V, while (2) ECL signal of Ru(bpy)3 2+ with tripropylamine as co-reactants displays one band at 620 nm at +0.95 V.Furthermore, the simultaneous emission of luminol and Ru(bpy)3 2 (RET-ECL system) was analysed using a microspectrometer detector [3]. ECL spectra display three emission bands at 420, 510 and 620 nm. According to the previous experiments, bands at 420 and 510 nm should be associated with luminol due to its band emission is located from 350 to 600 nm, while band at 620 nm corresponds to Ru(bpy)3 2+. Nevertheless, Ru(bpy)3 2+ shows a characteristic absorption band at 450 nm, so minimum observed at this wavelength in the spectra is related to the Ru(bpy)3 2+ absorption. It demonstrates that bands at 420 and 510 nm are not really two bands, they form the characteristic band of luminol at 350-600 nm but is separated due to the characteristic absorption of Ru(bpy)3 2+ at 450 nm. Then, it is clear than Ru(bpy)3 2+ absorbs part of ECL emission of luminol before producing their own emission at more positive potentials. Spectro-electrochemiluminescence results demonstrates that the interaction between luminol and Ru(bpy)3 2+ is an important effect to be considered when ECL system is formed by these two luminophores.