Marsh grassbird

{{Short description|Species of bird}}

{{One source|date=December 2021}}

{{Speciesbox

| name = Marsh grassbird

| status = NT

| status_system = IUCN3.1

| status_ref = {{cite iucn |author=BirdLife International |date=2017 |title=Helopsaltes pryeri |volume=2017 |page=e.T22715480A117654950 |doi=10.2305/IUCN.UK.2017-3.RLTS.T22715480A117654950.en |access-date=11 November 2021}}

| image = Marsh Grassbird.jpg

| genus = Helopsaltes

| species = pryeri

| authority = (Seebohm, 1884)

| synonyms = Megalurus pryeri
Locustella pryeri

}}

The marsh grassbird (Helopsaltes pryeri), also known as the Japanese swamp warbler, is a species of Old World warbler in the family Locustellidae. It is found in China, Japan, South Korea, Mongolia, and Russia.

Its natural habitat is swamps. It is threatened by habitat loss.