| Systems Integration Office | Space Science | SIO |
| Silicon Oxide | Chemistry | SIO |
| Safetower International Organization | Organization | SIO |
| site intelligence officer | Government | SIO |
| silica | Government | SIO |
| Surety Information Office | Stock Exchange | SIO |
| Serious Inquiries Only | Job Title | SIO |
| Social Investment Organization | Community | SIO |
| Smithton, Tasmania, Australia | Regional Airport Code | SIO |
| Students Islamic Organisation of India | University | SIO |
| Standard Installation Organization | Military | SIO |
| Skidaway Institute of Oceanography | Ocean Science | SIO |
| Smithton | Airport Code | SIO |
| senior intelligence officer | Government | SIO |
| Serial Input/Output | Computing | SIO |
| Scientific or Industrial Organization (ITU member) | Computer and Networking | SIO |
| Subscribers In Operation | Telecommunication | SIO |
| supporting intelligence office, 8 | Government | SIO |
| Siouan Languages | Regional 3 Letter LanguageCode | SIO |
| Scripps Institution of Oceanography | Ocean Science | SIO |
| Senior Investigating Officer | Police | SIO |
| Special Information Operations | Military and Defence | SIO |
| signal intelligence officer | Government | SIO |
| system integration office | Government | SIO |
| Scalable Input/ Output Initiative | Computing | SIO |
