A prosthesis for lower-limb amputees having a foot segment and a tibial segment pivotally connected to each other about an articulation axis that perform an ankle joint of a leg/foot prosthesis. The leg-foot prosthesis has a gear motor whose axis coincides with the axis of the tibia. From the gear motor a pinion gear extends below with conical toothed shape that meshes with a toothed arch present on the foot. This way, the gear motor operates the relative movement between tibia and foot and varies the relative angle &thetas；. The gear motor can be associated with a microprocessor that is adapted to control the movement of the ankle joint. To obtain that, the microprocessor communicates with a position transducer provided at the articulation axis of the ankle that measure the rotation of the ankle, i.e. the angle &thetas；.
