A support bracket for cable trays, said support bracket being formed by a one-piece body made of a polymer material and comprising: - a base for fixing said support bracket to a vertical support surface; and - an arm extending in a cantilever manner from said base and comprising: an upper wall with an oblong upper face extending in a horizontal plane in a horizontal longitudinal direction of said arm , with respect to a usage position of said support bracket in which said support bracket is fixed by said base to said vertical support surface, said upper face of the arm forming a seating surface for a cable tray which is seated on said upper face of the arm; a lower wall opposite said upper wall ; and a central partition joining said upper wall and said lower wall ; wherein said central partition has at least one through opening adjacent to said upper wall ; characterised in that said upper wall is provided with through holes for the passage of fixing screws for fixing the cable tray to said support bracket ; and said at least one through opening is located below at least one of said through holes , such that said through opening contains an empty space into which said through hole comes, said empty space being a rectangular parallelepiped with a width (W), in said horizontal longitudinal direction of the arm , greater than or equal to 4 cm, and a height (H), in a vertical direction orthogonal to said horizontal longitudinal direction, greater than or equal to 2 cm. - a base for fixing said support bracket to a vertical support surface; and - an arm extending in a cantilever manner from said base and comprising: an upper wall with an oblong upper face extending in a horizontal plane in a horizontal longitudinal direction of said arm , with respect to a usage position of said support bracket in which said support bracket is fixed by said base to said vertical support surface, said upper face of the arm forming a seating surface for a cable tray which is seated on said upper face of the arm; a lower wall opposite said upper wall ; and a central partition joining said upper wall and said lower wall ; wherein said central partition has at least one through opening adjacent to said upper wall ; characterised in that said upper wall is provided with through holes for the passage of fixing screws for fixing the cable tray to said support bracket ; and said at least one through opening is located below at least one of said through holes , such that said through opening contains an empty space into which said through hole comes, said empty space being a rectangular parallelepiped with a width (W), in said horizontal longitudinal direction of the arm , greater than or equal to 4 cm, and a height (H), in a vertical direction orthogonal to said horizontal longitudinal direction, greater than or equal to 2 cm. a lower wall opposite said upper wall ; and a central partition joining said upper wall and said lower wall ; wherein said central partition has at least one through opening adjacent to said upper wall ; characterised in that said upper wall is provided with through holes for the passage of fixing screws for fixing the cable tray to said support bracket ; and said at least one through opening is located below at least one of said through holes , such that said through opening contains an empty space into which said through hole comes, said empty space being a rectangular parallelepiped with a width (W), in said horizontal longitudinal direction of the arm , greater than or equal to 4 cm, and a height (H), in a vertical direction orthogonal to said horizontal longitudinal direction, greater than or equal to 2 cm. <EOS>