Abstract: The present invention relates to a modular upright for building structures and a sliding safety grille which can be obtained by assembling these uprights. In a preferred embodiment, the modular upright (10) comprises a pair of anti-cutting reinforcing elements (1) which are lined by U-shaped modular elements (3) alternating with joining elements (2) and fastened together by at least one anti-pulling element (6) sliding vertically between two joining elements (2), in the space between the surface of the reinforcing elements (1) and the U-shaped modular elements (3).