Abstract: Rotary hydraulic actuator comprising a vane (1) which is mounted rotatably and sealingly in a chamber (2) made in a body (3) and on the faces of which a hydraulic fluid pressure is exerted, the vane being fixed mechanically to an element to be driven in rotation; the vane (1) comprises two parts (4, 5) extending radially on either side of its axis of rotation (XX), and these two parts are each movable in a chamber (8, 9) extending over an angular sector less than half a circumference, this chamber being divided into two compartments by the said part (4, 5); the actuator has a hydraulic circuit for feeding the chambers (8, 9), which is designed so as to be capable of driving the vane (1) in rotation in one direction or the other. This arrangement reduces the overall size of the actuator and increases its reliability.