A novel two-step method was developed to synthesize gold nanoparticles on boron-doped diamond (BDD) electrode. It consisted of sputter deposition of maximum 15 equivalent monolayers of gold, followed by a heat treatment at 400–600 °C in air. The as-sputtered gold deposits were highly dispersed (estimated particle size of 2–7 nm) but also unstable, a continuous potential cycling in the stability region of sulfuric acid leading to complete loss of the deposited gold. Subsequent heat treatment of as-sputtered deposits resulted in formation of a stable population of nanosized gold particles characterized by scanning electron microscopy and cyclic voltammetry. Gold nanoparticles with an average size of 15–35 nm could be prepared by this method on polycrystalline BDD film electrode, the particle size being dependent of the deposited amount. The invariant voltammetric response of the heat-treated gold deposits confirmed their applicability for electrocatalysis.