| Demini River | |
| Pushpin Map: | Brazil |
| River System: | Rio Negro |
| Mouth Location: | Rio Negro |
| Mouth Coordinates: | -0.7728°N -62.9413°W |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
| Tributaries Left: | Toototobi River |
| Tributaries Right: | Cuieiras River, Araçá River |
Demini River is a river in the Amazon rainforest of the state of Amazonas, Brazil. It is a tributary of the Rio Negro.
The Demini River rises in the Serra do Aracá State Park, a conservation unit created in 1990.It flows southwest through the park, then flows south to join the Rio Negro.The Toototobi River is a tributary of the upper part of the Demini near the headwaters of the Orinoco near the border of Venezuela. The Yanomami índios are native to this area.