A lifting system for leaves of furniture that oscillate about at least one horizontal axis between a closed position and a raised open position, the lifting system comprising a supporting body which can be connected to a fixed portion (11, 12) of the piece of furniture, a system of articulated levers which connect said supporting body to a leaf of the piece of furniture, said system of levers comprising a first lever which has an end connected rotatably to said supporting body by way of a rotation pin and a second lever which has an end that can be connected rotatably to an element for fixing on said leaf of the piece of furniture, said first lever and said second lever being mutually articulated at the respective other ends, and elastic actuation means (24, 26) which are functionally connected to said system of articulated levers in order to generate a rotation torque for said system of levers, and means for increasing said rotation torque, which cooperate with said elastic actuation means (24, 26) in order to increase said rotation torque at least along a portion of the oscillation in the direction for opening the leaf that includes the raised position of the leaf, characterized in that said means for increasing the torque comprise cam means (23, 25) provided on at least one of said levers (17, 19) of the system of articulated levers, said cam means comprising a cam element connected to said first lever of the system of articulated levers and wherein said elastic actuation means are arranged between said supporting body and said first lever and are functionally connected to said cam element, said elastic means comprising: - a first portion, connected rotatably to said supporting body, - a second portion, connected to said first portion so that it can slide along a longitudinal axis, said second portion being connected also to said first lever of the system so that it can rotate and slide at a point of the first lever that is spaced apart from the rotation pin of said lever, said sliding and rotating connection between the second portion of the first elastic means and the first lever of the system of levers being provided with a pivot which is integral with said first lever, - at least one axially deformable elastic element, interposed between said first portion and said second portion, and - a sliding or rolling means connected to said second portion, shaped and arranged so as to act on said cam means. - a first portion, connected rotatably to said supporting body, - a second portion, connected to said first portion so that it can slide along a longitudinal axis, said second portion being connected also to said first lever of the system so that it can rotate and slide at a point of the first lever that is spaced apart from the rotation pin of said lever, said sliding and rotating connection between the second portion of the first elastic means and the first lever of the system of levers being provided with a pivot which is integral with said first lever, - at least one axially deformable elastic element, interposed between said first portion and said second portion, and - a sliding or rolling means connected to said second portion, shaped and arranged so as to act on said cam means.