A hybrid propulsion road vehicle having: a couple of rear driving wheels; a thermal internal combustion engine; a gearbox, which is arranged in rear position, receives motion from the thermal internal combustion engine and transmits motion to the rear driving wheels, and comprises a gear case housing all the moving parts; a reversible electric machine mechanically connectable to the rear driving wheels; an electric drive controlling the electric machine; and an accumulating system, which is able to store electric energy, is connected to the electric drive and is placed beside the gear case and on the opposite sides of the gear case so as not to longitudinally exceed the extension of the gear case itself.