Modification of boron-doped diamond (BDD) with gold nanoparticles (AuNPs) has been developed for an arsenic sensor. The AuNPs was synthesized using garlic extract served as both the capping and reducing agents. The optimum mixture of preparation was 0.11 moles of Au from HAuCl4 in 4 μ g of garlic extract at pH 5 under 15 min UV irradiation. TEM Image showed that the average size of AuNPs was varied from 2-10 nm, which was also confirmed by UV-Vis spectra at 520 nm. Furthermore, the synthesized AuNPs were immobilized on the BDD surface by immersion technique under UV irradiation at 254 nm. SEM EDX showed that AuNPs-modified BDD with an Au:C ratio of 37:63 (wt.%) could be successfully prepared. Application of the AuNPs-modified BDD for detection of As3+ ions using anodic stripping voltammetry technique showed that green synthesized process of BDD modification was suitable to prepare an electrode for arsenic sensors.