The Straight-billed Reedhaunter (Limnoctites rectirostris) is a South American bird species in the family Furnariidae. It is today placed in the monotypic genus Limnoctites.

Formerly it was "? and in some works it still is "? placed in Limnornis, but it seems closer to the typical spinetails (Cranioleuca) than to the Curve-billed Reedhaunter (Limnornis curvirostris) which lives in the same general region and habitat, and thus shares some adaptations with L. rectirostris. The modern treatment makes Limnornis monotypic also. As using monotypic genera if not really necessary is eschewed by most taxonomists today, the Straight-billed Reedhaunter is liable to be placed in Cranioleuca if further studies verify its placement.

This bird is found in north-eastern Argentina, south-eastern Brazil and Uruguay. In its range it is essentially limited to marshy areas in the pampas and planalto grasslands, preferring localities with abundant growth of spiny eryngos (Eryngium spp.). Its numbers are decreasing and is becoming rare due to habitat loss.