Here, we designed a Mn3O4/CuOx heterostructure supported on copper foil (CF) for electrocatalytic nitrate reduction to ammonia. The selectivity and Faraday efficiency of ammonia were 96.79% and 86.55%, respectively. Multiple characterizations revealed that Mn3O4/CuOx/CF showed faster charge transfer and created more electron-deficient Mn sites, electron-rich Cu sites and large numbers of oxygen vacancies, which were conducive to improving the catalytic activity. This work may open an avenue for the construction of heterostructures as an electrocatalyst for the reduction of nitrate to ammonia.