A woman died and a man suffered life-threatening injuries when their car left the road and overturned on the A27 near Pevensey on Friday night.
Emergency services were called to the scene at the point where Hankham Hall Road crosses the A27 around 7.30pm.
A 35-year-old woman from Bexhill who was a passenger in the white Ford Fiesta ST was declared dead at the scene.
The driver, a 37-year-old man from St Leonards-on-Sea, was taken to the Royal Sussex County Hospital in Brighton with life-threatening injuries.
Sergeant Richard Hobbs from the Surrey and Sussex Roads Policing Unit said: "This is a tragic incident and we are seeking witnesses as to what happened".
The road, which was closed while rescue, recovery and investigations were carried out, was re-opened around 5.15am.