Oio is a region in Guinea-Bissau. Its capital is Farim. Other major cities and towns include Nhacra, Mansoa, Bissorã and Cumeré. The region borders Senegal to the north, the Guinea-Bissau regions of Bafatá, Bissau and Biombo to the east, the Rio Geba/Guinea-Bissau region of Quinara to the south and the Guinea-Bissau region of Cacheu to the west.
The Rio de Canjambari flows through the north of the region.
One of the highest place in Oio is Tambandinto with an elevation of 70 m.
Oio is divided into five sectors: