| Itajaí-Açu river | |
| Pushpin Map: | Brazil |
| Source1 Location: | Santa Catarina state |
| Mouth Location: | Atlantic Ocean |
| Mouth Coordinates: | -26.912°N -48.642°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
The Itajaí-Açu River is a river in the state of Santa Catarina in southeastern Brazil. It flows into the Atlantic Ocean near the city Itajaí.
The river basin includes part of the Canela Preta Biological Reserve, a full protected area.