Mangatewainui River

{{Use New Zealand English|date=April 2024}}

{{Use dmy dates|date=July 2019}}

{{Infobox river

| name = Mangatewainui River

| image =

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| source1_location =

| mouth_location = Manawatu River

| subdivision_type1 = Country

| subdivision_name1 = New Zealand

| length_km = 27

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}}

The Mangatewainui River is a river of the Manawatū-Whanganui 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 {{convert|8|km|mi|0}} east of Dannevirke.

The Mangatewainui River should not be confused with its northern neighbour, the Mangatewai River.