Oriximiná is the westernmost and second-largest (by territorial area) municipality in the Brazilian state of Pará.

The city lies on the Trombetas river, 40 kilometres (25 mi) northwest of Óbidos.

The north of the municipality contains the larger part (75.89%) of the 4,245,819 hectares (10,491,650 acres) Grão-Pará Ecological Station, the largest fully protected tropical forest conservation unit on the planet.

[3] The municipality also contains the 1,007,580 hectares (2,489,800 acres) Rio Trombetas Biological Reserve, a strictly protected conservation unit created in 1979 to preserve the ecology and specifically to protect the Arrau turtle.

[4] The municipality contains part of the Saracá-Taquera National Forest, a 441,283-hectare (1,090,430-acre) sustainable-use conservation unit created in 1989.