- Observatory
- Obwandiyag (Pontiac)
- Obwandiyag (Pontiac): Warrior Chief
- Occupational Diseases
- Ocean
- Ocean Current
- Ocean Falls
- Ocean Industry
- Ocean Mining
- Ocean Ranger
- Ocean Wave Energy
- Oceanography
- Octave Chatillon
- Octave Crémazie
- Octave-Henri Julien
- Octavia Grace Ritchie
- October Crisis
- Octobre
- Octopus
- Odawa