A sliding fire door to be installed at a passageway obtained through a wall of a building, the sliding fire door comprising: - at least one sliding panel arranged for closing said passageway; - at least one support and sliding upper linear guide of said at least one sliding panel, said at least one upper linear guide being configured to be fixed to said wall at said passageway, being positioned above said at least one sliding panel and being oriented along a first direction which is substantially horizontal and parallel with respect to a walking surface; - one or more sliding means, fixed above said at least one sliding panel and slidingly engaged with said at least one upper linear guide to allow said at least one sliding panel to translate, along said first horizontal direction, between an opening position and a closing position of said passageway and vice versa; - at least one support and sliding lower linear guide of said at least one sliding panel, said at least one lower linear guide being configured to be fixed on said walking surface at said passageway, being positioned below said at least one sliding panel and being oriented along a second horizontal direction which is parallel and coplanar with respect to said first horizontal direction; and - one or more guide means, fixed below said at least one sliding panel and engageable with said at least one lower linear guide, wherein said at least one lower linear guide comprises one or more box-shaped channels, wherein each box-shaped channel comprises at least one upper wall which is provided with at least one elongated slot oriented along said second horizontal direction, and wherein each guide means consists of an elongated profile, oriented along said second horizontal direction and having an inverted T shape in cross section, said elongated profile comprising at least one vertical flat portion, which forms the stem of the inverted T and is arranged to slidably fit into said elongated slot, and at least one horizontal flat portion, which forms the head of the inverted T and is arranged to slide within said box-shaped channel at a predefined distance below said upper wall, the sliding fire door being characterized in that said one or more box-shaped channels are arranged to be buried below said walking surface, wherein said at least one upper wall of each box-shaped channel is arranged to be coplanar with respect to said walking surface, and in that one or more ducts (50, 52) are provided inside said one or more box-shaped channel for supplying air and/or water at a predefined pressure inside said one or more box-shaped channel. - at least one sliding panel arranged for closing said passageway; - at least one support and sliding upper linear guide of said at least one sliding panel, said at least one upper linear guide being configured to be fixed to said wall at said passageway, being positioned above said at least one sliding panel and being oriented along a first direction which is substantially horizontal and parallel with respect to a walking surface; - one or more sliding means, fixed above said at least one sliding panel and slidingly engaged with said at least one upper linear guide to allow said at least one sliding panel to translate, along said first horizontal direction, between an opening position and a closing position of said passageway and vice versa; - at least one support and sliding lower linear guide of said at least one sliding panel, said at least one lower linear guide being configured to be fixed on said walking surface at said passageway, being positioned below said at least one sliding panel and being oriented along a second horizontal direction which is parallel and coplanar with respect to said first horizontal direction; and - one or more guide means, fixed below said at least one sliding panel and engageable with said at least one lower linear guide,