OCA
- 2-Chloroamphetamine
- Cerro Armazones Observatory
- Court of Appeal for Ontario
- Croton Aqueduct
- Côte d'Azur Observatory
- Diocese of Oca (Asia Minor)
- Iruña de Oca
- Liquid optically clear adhesive
- OCA1
- Oakland Charter Academy
- Oca (river)
- Oca (structure)
- Oculocutaneous albinism
- Odisha Cricket Association
- Odoo
- Offensive counter air
- Office of Consumer Affairs (Canada)
- Oka (disambiguation)
- Olympic Council of Asia
- Ontario College of Art
- Open College of the Arts
- Open Content Alliance
- Open Control Architecture
- Open coloring axiom
- Operation Crossroads Africa
- Optical clearing agent
- Optimum currency area
- Oracle Certification Program
- Orange County Airport
- Orange County Astronomers
- Oregon Citizens Alliance
- Oregon Coast Aquarium
- Organic Consumers Association
- Organised and Financial Crime Agency of New Zealand
- Organization of Chinese Americans
- Organized Crime Agency of British Columbia
- Orthodox Church in America
- Outback Communities Authority
- Oxalis tuberosa
- Oxford Capacity Analysis
- Oxford Conservative Association
- Villafranca Montes de Oca