A supporting counter-frame for sliding doors with an automatic closing system comprising, for each sliding door (2), a first pulley (11), a second pulley (12), a counterweight (15) equipped with a third pulley (16) and a motion transmission cable (28); said counterweight (15) is housed within a vertical section bar (4) of the counter-frame (1); one end of the cable (28) is fixed to a trolley (24) of a sliding door (2) and slides till the first pulley (11) along the sliding direction of the sliding door (2), from the first pulley (11) to the second pulley (12) horizontally and orthogonally to the sliding movement of the sliding door (2) and finally from the second pulley (12) to the third pulley (16) of the counterweight (15) and again to the second pulley (12) vertically and orthogonally to the sliding movement of the sliding door (2).