Óc Eo (Vietnamese) is an archaeological site in modern-day Óc Eo commune of Thoại Sơn District in An Giang Province of southern Vietnam. Located in the Mekong Delta, Óc Eo was a busy port of the kingdom of Funan between the 2nd century BC and 12th century AD and it may have been the port known to the Greeks and Romans as Cattigara.

Scholars use the term Óc Eo culture to refer to the archaeological culture of the Mekong Delta that is typified by the artifacts recovered at Óc Eo through archaeological investigation.

Excavation at Óc Eo began on 10 February 1942, after French archaeologists had discovered the site through the use of aerial photography. The first excavations were led by Louis Malleret, who identified the site as the place called Cattigara by Roman merchants in the first centuries of the Roman Empire. The site covers 450 hectares.

Óc Eo is situated within a network of ancient canals that crisscross the low flatland of the Mekong Delta. One of the canals connects Óc Eo to the town's seaport while another goes 68 kilometres (42 mi) north-northeast to Angkor Borei. Óc Eo is longitudinally bisected by a canal, and there are four transverse canals along which pile-supported houses were perhaps ranged.

Archaeological sites reflecting the material culture of Óc Eo are spread throughout southern Vietnam, but are most heavily concentrated in the area of the Mekong Delta to the south and west of Ho Chi Minh City. The most significant site, aside from Óc Eo itself, is at Tháp Muời north of the Tiền Giang River, where among other remains a stele with a 6th-century Sanskrit text has been discovered.

Aerial photography in 1958 revealed that a distributary of the Mekong entered the Gulf of Thailand during the Funan period in the vicinity of Ta Keo, which was then on the shore but since then become separated from the sea by some distance as a result of siltation. At that time, Ta Keo was connected by a canal with Óc Eo, allowing it access to the Gulf. The distributary of the Mekong revealed in the aerial photography was probably the Saenus mentioned in Ptolemy’s Geography as the western branch of the Mekong, which Ptolemy called the Cottiaris. The Cattigara in Ptolemy's Geography could be derived from a Sanskrit word, either Kottinagara (Strong City) or Kirtinagara (Renowned City).

The remains found at Óc Eo include pottery, tools, jewelry, casts for making jewelry, coins, and religious statues. Among the finds are gold jewellery imitating coins from the Roman Empire of the Antonine period. Roman golden medallions from the reign of Antoninus Pius, and possibly his successor Marcus Aurelius, have been discovered at Óc Eo, which was near Chinese-controlled Jiaozhou and the region where Chinese historical texts claim the Romans first landed before venturing further into China to conduct diplomacy in 166. Many of the remains have been collected and are on exhibition in Museum of Vietnamese History in Ho Chi Minh City.

Among the coins found at Óc Eo by Malleret were eight made of silver bearing the image of the hamsa or Vietnamese crested argus, apparently minted in Funan.