Core shell Au@Pd nanoparticles modified at boron-doped diamond (AuPd-BDD) electrodes were successfully prepared. Pd shell was formed at Au nanoparticles (AuNP) by the reduction reaction of H2PdCl4 to produce purple Au@Pd nanoparticles. The characterization performed using UV-Visible spectrophotometer showed the maximum wavelength at 523 nm, which decreased with the formation of Pd shell. The AuPd was then deposited on N-BDD surfaces and characterized using scanning electron microscopy (SEM) and X-Ray photoelectron spectroscopy (XPS). The modified electrode was used to determine the oxygen dissolved in phosphate buffer solution (PBS) by using cyclic voltammetry technique. Comparison between voltammograms of AuPd-N-BDD and AuNP-N-BDD indicated that the deposition of Au@Pd nanoparticles on N-BDD was successfully performed.