System for the construction of building constructions in which there are provided walls defined by a plurality of prefabricated panels, arranged in superimposed horizontal rows, with each of said panels of the type comprising a reinforcing structure embedded in a casting of mixed building materials, with such reinforcing structure lying in the vertical median plane of said panel, parallel to its main faces, and consists of one or more vertical tubular members extended for the entire height of said prefabricated panel and outcropping the top and bottom horizontal sides, and two horizontal tubular elements, with said tubular elements, outcropping from opposite sides, with their free ends, in correspondence to the respective vertical sides, of the same panel, said system being characterized in that: - the two horizontal tubular elements (21,22) are rigidly coupled to said vertical tubular elements at intermediate height of these; and in that the system comprises: - at least two metal profiles,,, arranged vertically and locked to a foundation, adapted to define the ends of one of said walls, with each of said profiles,, adapted to form, firstly, a portion of a formwork for the casting of a pillar, and later intended to be embedded in said pillar after its realization, delimiting at least two vertical walls vertical of it; - a plurality of positioning and supporting means, with horizontal axis fixed to said metal profiles,, at predetermined heights, each of which protrudes outside of these and intended to engage and bind the corresponding end of said tubular horizontal element, of the reinforcing structure of a panel which is an end panel of one of said horizontal rows, abutting said profiles,,, said positioning and supporting means defining for the same panel a predetermined position; - horizontal connecting means, adapted to simultaneously engage the portions of the opposite horizontal tubular elements, of the reinforcing structures of two adjacent panels in the same row, in order to mutually constrain said adjacent panels; - vertical connecting means, adapted to simultaneously engage at least two superimposed and aligned vertical tubular members of the reinforcing structures of corresponding superimposed panels, in order to mutually constrain said superimposed panels. - the two horizontal tubular elements (21,22) are rigidly coupled to said vertical tubular elements at intermediate height of these; and in that the system comprises: - at least two metal profiles,,, arranged vertically and locked to a foundation, adapted to define the ends of one of said walls, with each of said profiles,, adapted to form, firstly, a portion of a formwork for the casting of a pillar, and later intended to be embedded in said pillar after its realization, delimiting at least two vertical walls vertical of it; - a plurality of positioning and supporting means, with horizontal axis fixed to said metal profiles,, at predetermined heights, each of which protrudes outside of these and intended to engage and bind the corresponding end of said tubular horizontal element, of the reinforcing structure of a panel which is an end panel of one of said horizontal rows, abutting said profiles,,, said positioning and supporting means defining for the same panel a predetermined position; - horizontal connecting means, adapted to simultaneously engage the portions of the opposite horizontal tubular elements, of the reinforcing structures of two adjacent panels in the same row, in order to mutually constrain said adjacent panels; - vertical connecting means, adapted to simultaneously engage at least two superimposed and aligned vertical tubular members of the reinforcing structures of corresponding superimposed panels, in order to mutually constrain said superimposed panels. - at least two metal profiles,,, arranged vertically and locked to a foundation, adapted to define the ends of one of said walls, with each of said profiles,, adapted to form, firstly, a portion of a formwork for the casting of a pillar, and later intended to be embedded in said pillar after its realization, delimiting at least two vertical walls vertical of it; - a plurality of positioning and supporting means, with horizontal axis fixed to said metal profiles,, at predetermined heights, each of which protrudes outside of these and intended to engage and bind the corresponding end of said tubular horizontal element, of the reinforcing structure of a panel which is an end panel of one of said horizontal rows, abutting said profiles,,, said positioning and supporting means defining for the same panel a predetermined position; - horizontal connecting means, adapted to simultaneously engage the portions of the opposite horizontal tubular elements, of the reinforcing structures of two adjacent panels in the same row, in order to mutually constrain said adjacent panels; - vertical connecting means, adapted to simultaneously engage at least two superimposed and aligned vertical tubular members of the reinforcing structures of corresponding superimposed panels, in order to mutually constrain said superimposed panels.