A slide rail assembly configured for being mounted to a rack , the rack comprising a first post and a second post , the slide rail assembly being configured to be mounted to the first post of the rack through a first bracket and to be mounted to the second post through a second bracket , the slide rail assembly comprising a rail member and a supporting device, the supporting device being configured for the rail member , and comprising: a first holding frame having a first supporting means comprising a first supporting part and a second supporting part , a supporting passage being defined by the first supporting part and the second supporting part ; and a second holding frame having a second supporting means comprising a third supporting part and a fourth supporting part 1014), the first supporting means and the second supporting means supporting each other; wherein the rail member is fixedly connected to the first holding frame , the first supporting part of the first holding frame supports the third supporting part of the second holding frame , and the second supporting part of the first holding frame supports the fourth supporting part of the second holding frame ; characterized in that the first holding frame further comprises a first side wall extendedly connected to two ends of the first supporting part and two ends of the second supporting part in order to form a first closed supporting structure, the second holding frame further comprises a second side wall extendedly connected to two ends of the third supporting part and two ends of the fourth supporting part in order to form a second closed supporting structure, and the first closed supporting structure and the second closed supporting structure support each other; wherein the rail member has a first side and a second side , the first side of the rail member is formed with a slide rail passage , the first holding frame is connected to the second side of the rail member , and the slide rail passage of the rail member accomodates a first rail in order to allow the first rail to slide within the slide rail passage of the rail member , and a second rail that is slidably connected to the first rail . a first holding frame having a first supporting means comprising a first supporting part and a second supporting part , a supporting passage being defined by the first supporting part and the second supporting part ; and a second holding frame having a second supporting means comprising a third supporting part and a fourth supporting part 1014), the first supporting means and the second supporting means supporting each other; wherein the rail member is fixedly connected to the first holding frame , the first supporting part of the first holding frame supports the third supporting part of the second holding frame , and the second supporting part of the first holding frame supports the fourth supporting part of the second holding frame ; characterized in that the first holding frame further comprises a first side wall extendedly connected to two ends of the first supporting part and two ends of the second supporting part in order to form a first closed supporting structure, the second holding frame further comprises a second side wall extendedly connected to two ends of the third supporting part and two ends of the fourth supporting part in order to form a second closed supporting structure, and the first closed supporting structure and the second closed supporting structure support each other; wherein the rail member has a first side and a second side , the first side of the rail member is formed with a slide rail passage , the first holding frame is connected to the second side of the rail member , and the slide rail passage of the rail member accomodates a first rail in order to allow the first rail to slide within the slide rail passage of the rail member , and a second rail that is slidably connected to the first rail . <EOS>