Dos Marmelos River is a river of Amazonas state in north-western Brazil. It is a tributary of the Madeira River, and merges into this river about 80 km upstream from the town of Manicoré. The headwaters of the river are in the Campos Amazônicos National Park, a 961318 ha protected area created in 2006 that holds an unusual enclave of cerrado vegetation in the Amazon rainforest.