The Nelson's Sharp-tailed Sparrow, Ammodramus nelsoni, is a small sparrow. Formerly, this bird and the Saltmarsh Sharp-tailed Sparrow were considered to be a single species, the Sharp-tailed Sparrow.

Adults have brownish upperparts with grey on the crown and nape, a cream-coloured breast with light or indistinct streaking and a white throat and belly; they have an orange face with grey cheeks and a short pointed tail.

Their breeding habitat is marshes on the Atlantic coast of Canada and Maine, central Canada, (the Canadian Prairies region), and the north central United States. The nest is an open cup attached to vegetation and close to the ground. Males compete for females but do not defend territories; they sometimes help feed the young.

These birds migrate to the southeastern coasts of the United States.

These birds forage on the ground or in marsh vegetation, sometimes probing in mud. They mainly eat insects, aquatic invertebrates and seeds.

The call is a raspy trill, almost a mechanical sound. It may be given in flight during the nesting season.

This bird was named after Edward William Nelson, an American naturalist.