The vehicle, driven by a 16-year-old girl, rolled off Rutledge Road near the town of Sydenham at around 10:45 p.m. Wednesday, said Ontario Provincial Police.
A girl and a boy, both 16, were pronounced dead at the scene.
A 17-year-old boy was taken to hospital with life-threatening injuries, while the driver and another 16-year-old girl suffered non-life-threatening injuries.
No names were released.
OPP Technical Traffic Collision investigators are aiding in the investigation.
Anyone with information about the crash is asked to contact Frontenac OPP at 613-372-1932.