Two Audis and a Toyota collided near Birdlip, just south of Cheltenham, at around 9.35pm with three people taken to Southmead Hospital with serious injuries.
Gloucestershire Police said a Hampshire woman who was a passenger in the Toyota died at the scene.
A police spokesman said: '˜Were you on A417 last night - northbound M5 and southbound M4/Swindon? If you witnessed anything and can help please call 101 inc 476 22/12.'