This paper reports on the influence of the surface termination (H-, HO-, NH₂-) of boron-doped diamond (BDD) electrodes on the oxygen reduction reaction (ORR) in alkaline solution. The aminated BDD surface displays a higher oxygen reduction current density and a positive shift in the oxygen reduction potential compared to H- and HO-terminated BDD surfaces. The behavior is most likely due to a preferential adsorption of oxygen species on the NH₂ termination. The ORR mechanism on the H-, HO-, and NH₂-terminated BDD surfaces was investigated for the first time using electrochemiluminescence (ECL) of luminol. The results indicate that the ORR proceeds via a two-electron process on H-terminated diamond, while a four-electron pathway is observed for oxidized and aminated BDD electrodes. We further show that the ECL approach can be easily extended to investigate the ORR mechanism on different electrodes and composite materials. The influence on the surface termination on the reduction of oxygen on gold-nanoparticle-modified BDD electrodes has been studied.