Ombai Strait (Indonesian: Selat Ombai, Portuguese: Estreito de Ombai, Tetum: Estreitu Ombai) is an international strait in Southeast Asia. It separates the Alor Archipelago (part of East Nusa Tenggara province) to the west from the islands of Wetar (part of Maluku Province) and Atauro (part of the nation of Timor Leste) to the east, and from Timor to the south, all these islands forming part of the Lesser Sunda Islands. The strait is also the western portion of a pair of international straits, the other one being Wetar Strait; the two straits combine to link the Pacific Ocean with the Indian Ocean.

Ombai is an alternative name for the island of Alor, in the Alor Archipelago on the other side of the strait's north, north western and western coastline.

In Tetum, the expression tasi feto (lit. transl. 'female sea') is often used to refer to the 'Ombai-Wetar Strait', which extends along most of Timor's northern shores. The counterpart of that body of water, the Timor Sea, which has larger waves, is more turbid, and washes the whole of Timor's southern coastline, is commonly referred to in Tetum as tasi mane (lit. transl. 'male sea').

Ombai Strait is relatively narrow and deep (3,250 m (10,660 ft)). It has complex and extreme bathymetry, ranging from narrow reef flats (often less than 60 m (200 ft) wide) partly covered with seagrass and coral, to 3,000 m (9,800 ft) depths within 20 km (12 mi) of the coast.

The strait separates the Alor Archipelago from the islands of Wetar, Atauro, and Timor in the Lesser Sunda Islands. It also straddles the boundary between the Banda Sea (in its north east) and the Savu Sea (in its south west).

The Alor Archipelago, and the western part of Timor except the coastal exclave of Oecusse, which is on the north coast of western Timor, are part of the province of East Nusa Tenggara, Indonesia. Wetar is part of the Maluku Province of Indonesia. Atauro, Oecusse, and the eastern part of Timor comprise the nation of Timor-Leste.

The southern limit of the Banda Sea runs along the southern edge of the strait from the eastern extremity of Timor along its north coast as far south west as longitude 125° East. From that point, the Banda Sea's western limit heads north to Alor Island, where it starts a further run, east, along Alor's south coast, around its east point, and beyond.

Meanwhile, Ombai Strait continues to run from longitude 125° East in a south westerly direction, now within the limits of the Savu Sea. It extends, as part of that sea, at least as far south west as Batek Island, at the north western tip of Oecusse.