The Olympic Athletic Center of Athens Spiros Louis (Greek: Ολυμπιακό Αθλητικό Κέντρο Αθηνών "Σπύρος Λούης", Olympiakó Athlitikó Kéntro Athinón "Spýros Loúis") or OACA (OAKA)), is a sport facilities complex located at Marousi, in the north section of the city.

The complex was revamped for the games under a design produced by the Spanish architect Santiago Calatrava.

The stadium, built in 1982 and extensively refurbished for the games in 2004, including the addition of a roof, hosted the athletics events and the soccer final, as well as the Opening Ceremony on August 13, 2004 and the Closing Ceremony on August 29, 2004.The venue also hosted the same events during the 2004 Summer Paralympics.

The arena was used for artistic gymnastics and trampolining and also hosted the finals of the basketball matches at the games.

While it was reported in 2008 that almost all of the Olympic venues utilized for the 2004 games, including certain facilities in the Sports Complex such as the velodrome and tennis center, have fallen into varying states of dereliction or disrepair, all of the facilities in the Athens Olympic Sports Complex are still in use today.