Two other adults and a child were also injured near Shipton-under-Wychwood last night.
Police say the fatal crash happened at about 8.20pm at the junction of the A361 and the B4437, involving a black BMW 118 and a black Land Rover Freelander.
Sadly, a 33-year-old woman, who was a passenger in the rear seat of the BMW, was declared dead at the scene.
Two other adults and a child, all of whom were in the BMW, were injured and taken to hospital for treatment.
A passenger in the Land Rover was also taken to hospital after sustaining injuries.
Neither of the drivers were hurt.
Investigating officer, PC Darren Baker of the Serious Collision Investigation Unit, said: “Tragically, this incident has resulted in the death of a woman, as well as causing injuries to a number of others.
“I would like to hear from anybody who was travelling in the area at the time and saw the cars involved, or who may have a dash-cam recording which could assist our investigation."
Witnesses are urged to contact Thames Valley Police on 101, quoting reference number 43210270109.