| O | OASIS | Others | |
| O | Oasis---Center for the Personal Growth & Crisis Intervention, Hospital Authority of HKSAR | Others | |
| O | Obscene Articles Tribunal, the Government of the Hong Kong SAR | Others | |
| O | Obstetrical and Gynaecological Society of Hong Kong | Others | |
| O | OC,HK Youth Service Leadership Award | Others | |
| O | Occupational Health Advisory Committee of Occupational Safety and Health Council | Statutory | |
| O | Occupational Health Advisory Committee, The Occupational Safety and Health Council | Others | |
| O | Occupational Health and Safety OHSAS 18001 Technical Committee, Hong Kong Quality Assurance Agency | Others | |
| O | Occupational Safety and Health Council | Others | |
| O | Occupational Therapist Board, Supplementary Medical Professions Council | Others | |
| O | Ocean Park | Statutory | |
| O | Ocean Park Conservation Foundation (OPCF) | Others | |
| O | Ocean Park Conservation Foundation (OPCF) Hong Kong | Others | |
| O | Ocean Park Conservation Foundation Hong Kong | Others | |
| O | Ocean Park Conservation Foundation, Hong Kong | Others | |
| O | Ocean Park Development Committee | Others | |
| O | Ocean Park Education Committee | Others | |
| O | Ocean Park, Animal Welfare, Ethics & Care Committee | Others | |
| O | Ocean Sciences of the Canadian Institute of Advanced Research: Earth System Science Programme | Others | |
| O | OCLC Board of Trustees | Others | |
