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.^[1] It then crosses the border into Amazonas, where it runs through the 150,465 hectares (371,810 acres) Guariba Extractive Reserve, created in 2005.^[2] Further north it meets the Aripuanã in the region between the Campos Amazônicos and Juruena national parks.

• List of rivers of Amazonas