Ostrinia marginalis is a moth in the Crambidae family. It was described by Walker in 1866. It is found in North America, where it has been recorded from Newfoundland and Maine west to Alberta, the Northwest Territories and Yukon. The habitat consists of boggs and marshes. The wingspan is 15–17 mm. The fore- and hindwings are dark brown with a white postmedial line. The larvae feed on Rumex and Polygonum species.