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 a 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 connecting rod-crank kinematic mechanism (210, 220) which is connected to said rod, and to said first anchoring portion so as to define an articulated quadrilateral, and wherein first blocking device further comprises: - an actuator which is suitable to impart a shift movement to said connecting rod-crank kinematic mechanism so as to vary the configuration of said connecting rod-crank kinematic mechanism (210, 220) between a blocked configuration, in which said connecting rod is aligned with said crank and said articulated quadrilateral is degenerated into a triangle thus defining a strut blocking the roll angle (α) of the rod, and at least one free configuration, in which said connecting rod is misaligned with respect to said crank and said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - release means to assist said actuator in the passage from said blocked configuration to said at least one free 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 a 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 connecting rod-crank kinematic mechanism (210, 220) which is connected to said rod, and to said first anchoring portion so as to define an articulated quadrilateral, and wherein first blocking device further comprises: - an actuator which is suitable to impart a shift movement to said connecting rod-crank kinematic mechanism so as to vary the configuration of said connecting rod-crank kinematic mechanism (210, 220) between a blocked configuration, in which said connecting rod is aligned with said crank and said articulated quadrilateral is degenerated into a triangle thus defining a strut blocking the roll angle (α) of the rod, and at least one free configuration, in which said connecting rod is misaligned with respect to said crank and said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - release means to assist said actuator in the passage from said blocked configuration to said at least one free configuration. - an actuator which is suitable to impart a shift movement to said connecting rod-crank kinematic mechanism so as to vary the configuration of said connecting rod-crank kinematic mechanism (210, 220) between a blocked configuration, in which said connecting rod is aligned with said crank and said articulated quadrilateral is degenerated into a triangle thus defining a strut blocking the roll angle (α) of the rod, and at least one free configuration, in which said connecting rod is misaligned with respect to said crank and said articulated quadrilateral has a non-degenerate configuration which leaves the rolling movements free; and - release means to assist said actuator in the passage from said blocked configuration to said at least one free configuration.