A car and a motorbike were involved in a collision in Meads Street, at the junction with Darley Road, at about 10.15am.
The motorcyclist, a 22-year-old local man, was airlifted to the Royal Sussex County Hospital with serious injuries, Sussex Police confirmed.
The driver of the car, a 24-year-old local woman, was not injured, police added.
Officers are now appealing for witnesses and anyone with relevant information to come forward to Sussex Police online, quoting serial 437 of 08/04.
The area was blocked off while emergency services worked but has now been cleared.
1. Emergency services attend serious collision in Eastbourne
Air ambulance on the scene Photo: Sussex News and Pictures
2. Emergency services attend serious collision in Eastbourne
Aftermath of the incident Photo: Sussex News and Pictures
3. Emergency services attend serious collision in Eastbourne
Emergency services on the scene. Photo: Megan Baker
4. Emergency services attend serious collision in Eastbourne
Emergency services on the scene. Photo: Megan Baker