Guariba River (Portuguese: Rio Guariba) is a river of the Mato Grosso and Amazonas states in north-western Brazil. It is a tributary of the Aripuanã River.

In Mato Grosso the river forms the eastern boundary of the northern half of the 164,224 hectares (405,810 acres) Guariba-Roosevelt Extractive Reserve, a sustainable use unit created in 1996. It then crosses the border into Amazonas, where it runs through the 150,465 hectares (371,810 acres) Guariba Extractive Reserve, created in 2005. Further north it meets the Aripuanã in the region between the Campos Amazônicos and Juruena national parks.

• List of rivers of Amazonas