A knee joint includes a knee member including a movable plate connected to and pressable toward a fixed seat, and an interspace formed between the fixed seat and the movable plate. An upper connecting unit disposed atop the knee member abuts against the movable plate. A pivot shaft is inserted threadedly into the knee member and is rotatable relative thereto. Pressing the upper connection unit against the movable plate constricts the interspace so that the pivot shaft is clamped tightly between the fixed seat and the movable plate, thereby restricting a relative rotation between the knee member and the pivot shaft. The movable plate is restored to its original position when unpressed.
