The adjustable prosthetic leg, which is connected between a thigh and an artificial foot, has a controller, a connecting mechanism, a hydraulic unit, and a shell. The connecting mechanism and the hydraulic unit are pivotally connected to the controller, and the shell is pivotally connected to the hydraulic unit. The connecting mechanism extends into a hydraulic cylinder of the hydraulic unit. The hydraulic cylinder is in communication with a reserve hydraulic cylinder and a brake hydraulic cylinder of the hydraulic unit. The prosthetic leg allows a user to climb up or go down the stairs and walk on uneven ground easily without falling down.