A cooling system for a vehicle with hybrid propulsion; the cooling system is provided with a hydraulic circuit, inside which a cooling fluid flows, and has: a main branch, which carries out the cooling of a heat engine and comprises at least a first pump mechanically operated by the heat engine, and at least one radiator which is hit by air when the vehicle is moving; and a secondary branch, which is connected in parallel to the main branch by means of a starting offtake and an arrival offtake, has no heat exchangers of the water/air type, carries out the cooling of a reversible electric machine which may be mechanically connected to the driving wheels, and of a first electronic power converter which controls the electric machine, and comprises at least a second pump electrically operated.