Abstract The electroreduction of NO 3 − to NO 2 − and NH 3 has been investigated using a polycrystalline Au electrode in 0.5 M NaNO 3 and CsNO 3 solutions with pH in the ranges 1.1–3.0 and 9.85–12.8. The reduction of NO 3 − does not occur significantly in the strongly acidic solutions with pH lower than 1.4 to 1.6: the current efficiency for the NO 3 − reduction is less than 5%. A further increase in pH significantly facilitates the NO 3 − reduction. In basic solutions the reduction of NO 3 − occurs predominantly: the current efficiency reaches the range 80 to 99%. In the case of NaNO 3 solutions the ratio of the current efficiencies for NH 3 and NO 2 − production, CE NH 3 /CE NO 2 − is nearly unity in the acidic solutions and 2 to 3 in basic solutions. On the other hand, in CsNO 3 solutions, the current efficiency of NO 2 − production becomes much higher and the CE NH 3 /CE NO 2 − is 1 to 0.5 at pH in the range 2.0–3.0 and 0.2 to 0.5 at pH in the range 10.0–12.7. Partially positively-charged Na or Cs adatoms underpotentially deposited (upd) on the Au electrode surface are believed to facilitate the adsorption of NO 3 − ions, resulting in the preferential reduction of NO 3 − .