Closing device of a fuel tank lid for vehicles, comprising: - a box with a hole, - a roto-translating pin provided with a head suitable for engaging a slot of the fuel tank lid, said roto-translating pin being disposed in said hole of the box in such a way to rotate and translate from a retracted closing position, wherein the head engages said slot of the lid, to an extracted opening position, wherein the head disengages the slot of the lid; said roto-translating pin comprising a stop seat provided with a stop edge; - spring means pushing said roto-translating pin in said extracted opening position; - a locking device cooperating with said roto-translating pin to go from a locking position, wherein said roto-translating pin is locked in said retracted closing position, to an unlocking position, wherein said roto-translating pin is released; said locking device comprises a lever hinged to said box by means of a first pin; said lever having an arm with a locking tooth suitable for being stopped against said stop edge of the stop seat of the roto-translating pin; - actuation means connected to said locking device to move said locking device in the locking position and in the unlocking position, said actuation means comprising a connection lever hinged to said box by means of a second pin and provided with a first arm connected to said locking device and a second arm; - an actuator suitable for actuating said actuation means; said actuator being connected to said second arm of the connection lever of the actuation means; wherein said roto-translating pin comprises a shoulder that protrudes radially from the roto-translating pin in order to be stopped against the internal wall of the box around the hole in such a way to stop the extraction travel of the roto-translating pin; characterized in that said closing device also comprises a seal gasket disposed around the hole of the box; said shoulder of the roto-translating pin being suitable for pressing against said seal gasket. - a box with a hole, - a roto-translating pin provided with a head suitable for engaging a slot of the fuel tank lid, said roto-translating pin being disposed in said hole of the box in such a way to rotate and translate from a retracted closing position, wherein the head engages said slot of the lid, to an extracted opening position, wherein the head disengages the slot of the lid; said roto-translating pin comprising a stop seat provided with a stop edge; - spring means pushing said roto-translating pin in said extracted opening position; - a locking device cooperating with said roto-translating pin to go from a locking position, wherein said roto-translating pin is locked in said retracted closing position, to an unlocking position, wherein said roto-translating pin is released; said locking device comprises a lever hinged to said box by means of a first pin; said lever having an arm with a locking tooth suitable for being stopped against said stop edge of the stop seat of the roto-translating pin; - actuation means connected to said locking device to move said locking device in the locking position and in the unlocking position, said actuation means comprising a connection lever hinged to said box by means of a second pin and provided with a first arm connected to said locking device and a second arm; - an actuator suitable for actuating said actuation means;