| Dos Marmelos River | |
| Pushpin Map: | Brazil |
| Source1 Location: | Campos Amazônicos National Park, Amazonas |
| Source1 Coordinates: | -8.6513°N -61.9728°W |
| Mouth Location: | Madeira |
| Mouth Coordinates: | -6.1476°N -61.7868°W |
| Basin Size: | [1] |
| Subdivision Type1: | Country |
| Subdivision Name1: | Brazil |
| Length: | 510km (320miles)[2] |
| River System: | Amazon |
| Progression: | Madeira → Amazon → Atlantic Ocean |
| Discharge1 Location: | Confluence of Madeira, Amazonas |
| Discharge1 Avg: | (Period: 1971–2000)[3] |
| Tributaries Left: | Preto, Maici |
| Tributaries Right: | Branco, Sepoti |
Dos Marmelos River (Portuguese: Rio dos Marmelos) is a river of Amazonas state in north-western Brazil. It is a tributary of the Madeira River, and merges into this river about 80km (50miles) upstream from the town of Manicoré.
The headwaters of the river are in the Campos Amazônicos National Park, a protected area created in 2006 that holds an unusual enclave of cerrado vegetation in the Amazon rainforest.