Oia may refer to:
- Oia, Spain, a municipality in Galicia, in the province of Pontevedra
- Oia, Greece, a small town on the island of Santorini
- Orphans International America, a charity that benefits orphans and abandoned children
- Ourilândia do Norte Airport, an airport with IATA identifier OIA.
- Orlando International Airport ("OIA" is a local abbreviation), which actually uses the letters MCO for its airport designation
- Oahu Interscholastic Association, an athletic association of public secondary schools on the island of Oahu, Hawaii
- Outdoor Industry Association, a trade association of businesses in the outdoor recreation industry
- Outer World Investigation Agency, a fictional organization in Mortal Kombat video games, abbreviated to OIA or OWIA
- Office of the Independent Adjudicator, the higher-education ombudsman in the UK
- Official Information Act 1982, a piece of New Zealand legislation
- Office of Intelligence and Analysis, the intelligence organization of the US Department of the Treasury
- Oia, a genus of spiders in the Linyphiidae family