Fixing system of slab-like elements, particularly for railings, balustrades and parapets, comprising: - at least one base body, configured to be placed and fixed on a generic installation surface, made in the form of a box-shaped profile with a substantially U-shaped cross-section, open at the upper part, defining a channel within which the lower portion of at least one protection slab-like element is inserted; - at least one lower support element mounted on the lower internal surface of said channel; - at least one lateral support and retaining element of said at least one slab-like element, mounted on a first internal lateral surface of said channel, wherein said at least one lateral support and retaining element comprises a plate pivoting around a fixed pin element; - a plurality of lateral support and retaining groups of said at least one slab-like element, mounted on a second internal lateral surface of said channel which faces said first internal lateral surface, each of said lateral support and retaining groups comprising: - a slider, characterised in that said slider is provided with a convex back surface, configured to slide on a corresponding concave portion of said second inner side surface, pivoting around a fixed pin element, said slider comprising a tab protruding towards the inside of said channel, and a pair of inclined surfaces (243, 244) that are mutually opposite with respect to said protruding tab, and further characterised by - a pair of wedges (245, 246), positioned so as to be mutually opposite with respect to said tab, each of said wedges (245, 246) having its own inclined surface (247, 248) adapted to slide on a respective inclined surface (243, 244) of said pair of inclined surfaces (243, 244) of said slider, a first wedge of said pair of wedges (245, 246) being clampable on said tab along a first clamping direction, by means of at least a first clamping member, a second wedge of said pair of wedges (245, 246) being clampable on said tab along a second clamping direction, substantially opposite to said first clamping direction, by means of at least one second clamping member, the adjustment of the clamping of said at least one first clamping member and of said at least one second clamping member allowing to modify, in synergy with the oscillation of said at least one lateral support and retaining element, the inclination of said slab-like element around a vertical plane to obtain the perpendicularity of said slab-like element. - at least one base body, configured to be placed and fixed on a generic installation surface, made in the form of a box-shaped profile with a substantially U-shaped cross-section, open at the upper part, defining a channel within which the lower portion of at least one protection slab-like element is inserted; - at least one lower support element mounted on the lower internal surface of said channel; - at least one lateral support and retaining element of said at least one slab-like element, mounted on a first internal lateral surface of said channel, wherein said at least one lateral support and retaining element comprises a plate pivoting around a fixed pin element; - a plurality of lateral support and retaining groups of said at least one slab-like element, mounted on a second internal lateral surface of said channel which faces said first internal lateral surface, each of said lateral support and retaining groups comprising: - a slider, characterised in that said slider is provided with a convex back surface, configured to slide on a corresponding concave portion of said second inner side surface, pivoting around a fixed pin element, said slider comprising a tab protruding towards the inside of said channel, and a pair of inclined surfaces (243, 244) that are mutually opposite with respect to said protruding tab, and further characterised by - a slider, characterised in that said slider is - a pair of wedges (245, 246), positioned so as to be mutually opposite with respect to said tab, each of said wedges (245, 246) having its own inclined surface (247, 248) adapted to slide on a respective inclined surface (243, 244) of said pair of inclined surfaces (243, 244) of said slider, a first wedge of said pair of wedges (245, 246) being clampable on said tab along a first clamping direction, by means of at least a first clamping member, a second wedge of said pair of wedges (245, 246) being clampable on said tab along a second clamping direction, substantially opposite to said first clamping direction, by means of at least one second clamping member, the adjustment of the clamping of said at least one first clamping member and of said at least one second clamping member allowing to modify, in synergy with the oscillation of said at least one lateral support and retaining element, the inclination of said slab-like element around a vertical plane to obtain the perpendicularity of said slab-like element.