Forecarriage of a rolling motor vehicle with three or four wheels, comprising: a forecarriage frame, at least a pair of front wheels (10',10") kinematically connected to each other and to the forecarriage frame by means of a kinematic roll mechanism, an anti-roll system comprising a rod having a first and a second end opposite each other which connect by means of hinging means (101 ', 101 "; 102', 102") a first and second anchoring portion of the forecarriage directly to each other, wherein at least one of said first and second anchoring portions is subject to roll movements of said two front wheels (10', 10 "), said anti-roll system comprising a first blocking device suitable to reversibly block a rotation angle (α) of said rod, said angle of rotation (α) corresponding to the roll angle of said rod, characterized in that said first blocking device comprises a kinematic connecting rod-crank (210, 220) which is respectively connected to said rod, and to said first anchoring portion so as to define an articulated quadrilateral, and wherein said first blocking device further comprises: - an actuator which is suitable to impart a shift movement to said a kinematic connecting rod-crank (210, 220) so as to vary the configuration of said kinematic connecting rod-crank (210, 220) between a blocked configuration, in which said articulated quadrilateral is substantially degenerated into a triangle thus defining a strut blocking the roll angle of the rod, and at least one free configuration, in which said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - stop means suitable to stop the rotation of said crank in a position corresponding to said blocked configuration in the passage between said free configuration and said blocked configuration. a forecarriage frame, at least a pair of front wheels (10',10") kinematically connected to each other and to the forecarriage frame by means of a kinematic roll mechanism, an anti-roll system comprising a rod having a first and a second end opposite each other which connect by means of hinging means (101 ', 101 "; 102', 102") a first and second anchoring portion of the forecarriage directly to each other, wherein at least one of said first and second anchoring portions is subject to roll movements of said two front wheels (10', 10 "), said anti-roll system comprising a first blocking device suitable to reversibly block a rotation angle (α) of said rod, said angle of rotation (α) corresponding to the roll angle of said rod, characterized in that said first blocking device comprises a kinematic connecting rod-crank (210, 220) which is respectively connected to said rod, and to said first anchoring portion so as to define an articulated quadrilateral, and wherein said first blocking device further comprises: - an actuator which is suitable to impart a shift movement to said a kinematic connecting rod-crank (210, 220) so as to vary the configuration of said kinematic connecting rod-crank (210, 220) between a blocked configuration, in which said articulated quadrilateral is substantially degenerated into a triangle thus defining a strut blocking the roll angle of the rod, and at least one free configuration, in which said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - stop means suitable to stop the rotation of said crank in a position corresponding to said blocked configuration in the passage between said free configuration and said blocked configuration. - an actuator which is suitable to impart a shift movement to said a kinematic connecting rod-crank (210, 220) so as to vary the configuration of said kinematic connecting rod-crank (210, 220) between a blocked configuration, in which said articulated quadrilateral is substantially degenerated into a triangle thus defining a strut blocking the roll angle of the rod, and at least one free configuration, in which said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - stop means suitable to stop the rotation of said crank in a position corresponding to said blocked configuration in the passage between said free configuration and said blocked configuration.