A hydraulic rotary actuator comprising: - a body comprising a central part with an annular wall that defines at least one cylindrical cavity with an axis (Xc) and two closing elements (12, 13), adapted to close respective open ends of said annular wall; - a piston, housed moving in the cylindrical cavity and adapted to separate, in said cavity, a first chamber and a second chamber which can be supplied with a pressurized hydraulic fluid, said piston having a through seat between a first end and a second end; and - a shaft, housed in the trough seat of the piston and mounted rotatable in the body about an axis of rotation (Xa), said shaft carrying at the end at least one connection flange; wherein the ends of the shaft are rotatably housed in seats produced in the closing elements (12, 13), wherein a section of the shaft is provided on the outer surface with a first thread adapted to engage a corresponding second thread produced on the surface of the seat of the piston, wherein the axis of rotation (Xa) of the shaft is arranged eccentric with an eccentricity (Ec) with respect to the axis (Xc) of the cylindrical cavity; wherein each of the two chambers (20, 21) is connectable to a source of a pressurized hydraulic fluid by means of specific hydraulic passages (22, 23), the actuator being characterized in that each hydraulic passage comprises a first section produced in the annular wall of the central part and a second section produced in the corresponding closing element (12, 13), said second section emerging on an inner face of said corresponding of closing element (12, 13) facing the corresponding chamber (20, 21). - a body comprising a central part with an annular wall that defines at least one cylindrical cavity with an axis (Xc) and two closing elements (12, 13), adapted to close respective open ends of said annular wall; - a piston, housed moving in the cylindrical cavity and adapted to separate, in said cavity, a first chamber and a second chamber which can be supplied with a pressurized hydraulic fluid, said piston having a through seat between a first end and a second end; and - a shaft, housed in the trough seat of the piston and mounted rotatable in the body about an axis of rotation (Xa), said shaft carrying at the end at least one connection flange; wherein the ends of the shaft are rotatably housed in seats produced in the closing elements (12, 13), wherein a section of the shaft is provided on the outer surface with a first thread adapted to engage a corresponding second thread produced on the surface of the seat of the piston, wherein the axis of rotation (Xa) of the shaft is arranged eccentric with an eccentricity (Ec) with respect to the axis (Xc) of the cylindrical cavity; wherein each of the two chambers (20, 21) is connectable to a source of a pressurized hydraulic fluid by means of specific hydraulic passages (22, 23), the actuator being characterized in that each hydraulic passage comprises a first section produced in the annular wall of the central part and a second section produced in the corresponding closing element (12, 13), said second section emerging on an inner face of said corresponding of closing element (12, 13) facing the corresponding chamber (20, 21).