A demonstrator may be:
- A person performing a demonstration, such as to explain science or technology
- An attendee at a political rally
- A device or object used to perform a demonstration
- An academic rank
- A vehicle adapted to emergency service specification, and issued to locations for use as a prospective emergency vehicle if adopted to that workforce either police, ambulance or fire.
- A fountain pen with a transparent body originally used so dealers could show customers how they worked. See Demonstrator pen