West Yorkshire Police are appealing for witness to the accident on Torre Lane, east Leeds, yesterday to come forward.
Officers were called to the road in Harehills after reports of a collision involving a green Ford Focus and a pedestrian just after 5pm.
A police spokesperson said: "The Ford Focus was heading towards Lupton Avenue when it collided with the 12 year old pedestrian.
The 12 year old boy has suffered serious and potentially life threatening injuries.
Officers are appealing for anyone who witnessed the collision or saw the green Ford Focus before the collision to come forward.