A safety post for making protective fencings in construction sites, comprising a tubular cylindrical body (13) in which a bottom base (13a) and a top base (13b) are defined, said body (13) being hollow at least over a section (15) opening at the bottom base (13a) so as to allow fitting the post onto one of the reinforcement iron rods generally present in a building structure under construction, said body (13) further including a number of brackets (17) in order to bear as many boards, bars, crosspieces and the like that will form the protective fencing, and a screw or bolt (19), extending into the body (13) through a threaded hole (21) near the bottom base (13a) of the body (13), in order to firmly lock said iron rod inside the body (13).