Officers were called to the A26 just south of Southease railway station at 9.55am on Tuesday (13 April) after a lorry and a blue Yahama motorcycle collided.
The motorcyclist – a 57-year-old man from Seaford – was tragically pronounced dead at the scene. The driver of the lorry was unharmed.
Officers are appealing to anyone who witnessed what happened or has relevant dash-cam footage of either vehicle prior to the collision to come forwards.
The A26 has been partially closed while enquiries are ongoing and travel disruption is likely to continue for the remainder of the afternoon.
Anyone with information can report online or call 101, quoting Operation Darkstar.