| O | OCLC Global Council | Others | |
| O | Odyssey of the Mind Hong Kong Regional Tournament 2017 | Others | |
| O | Odyssey of the Mind Hong Kong Regional Tournament 2018 | Others | |
| O | OECD Learning Compass for 2030 | Others | |
| O | OECD-Centre for Educational Research and Innovation (CERI) | Others | |
| O | of the Board Education Committee of the Chinese International School Foundation | Others | |
| O | Office for Film, Newspaper and Article Administration | Others | |
| O | Office of International Student Exchange, H. K. U. | Deleted | |
| O | Office of Public Health and Environmental Hazards, the US Department of Veterans Affairs, Washington DC, USA | Others | |
| O | Office of Telecommunication Authority | Others | |
| O | Office of the Commissioner for Administrative Complaints | Others | |
| O | Office of the Communications Authority - Telecommunications Regulatory Affairs Advisory Committee | Others | |
| O | Office of the Compliance Advisor Ombudsman (CAO), International Finance Corporation/World Bank Group- Asian Mediation Consultation Group | Others | |
| O | Office of the Ombudsman | Others | |
| O | Office of the Ombudsman for UN Funds and Programs | Others | |
| O | Office of the Privacy Commissioner for Personal Data | Others | |
| O | Official Languages Division, Civil Service Bureau, HKSAR | Others | |
| O | OLQE Committee, The Law Society of Hong Kong | Others | |
| O | Ombudsman | Others | |
| O | OMICS groups, USA | Others | |
