The Mangatewainui River is a river of the Manawatu-Wanganui Region of New Zealand's North Island. An upper tributary of the Manawatu River, it flows generally southeast from its sources in the Ruahine Range northwest of Norsewood, and meets the young Manawatu River eight kilometres east of Dannevirke.
The Mangatewainui River should not be confused with its northern neighbour, the Mangatewai River.
"Place Name Detail: Mangatewainui River". New Zealand Geographic Placenames Database. Land Information New Zealand. Retrieved 12 July 2009.
Coordinates: 40°11′S 176°12′E / 40.183°S 176.200°E