| Pacaás Novos River | |
| Pushpin Map: | Brazil |
| River System: | Mamoré River |
| Source1 Location: | Rondônia state |
| Source1 Coordinates: | -10.8487°N -63.6327°W |
| Mouth Coordinates: | -10.8583°N -65.2776°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
| Tributaries Right: | Ouro Preto River |
The Pacaás Novos River (Portuguese: Rio Pacaás Novos) is a river of Rondônia state in western Brazil.It is a tributary of the Mamoré River, which it joins from the right just above Guajará-Mirim.
The Pacaás Novos River rises in the mountains in the west of the Pacaás Novos National Park and flows west from there through the Rio Pacaás Novos Extractive Reserve.The Ouro Preto River, a right tributary that flows from the east through the Rio Ouro Preto Extractive Reserve, joins the Pacaás Novos River on the west boundary of the reserve, which is defined by this section of the Pacaás Novos.