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 (1000, 1200) 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 (1002, 1202) 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 (1000, 1200), the first supporting part of the first holding frame (1000, 1200) supports the third supporting part of the second holding frame (1002, 1202), and the second supporting part of the first holding frame (1000, 1200) supports the fourth supporting part of the second holding frame (1002, 1202); characterized in that the first holding frame (1000, 1200) 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 (1002, 1202) 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 (1000, 1200) 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 (1000, 1200) 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 (1002, 1202) 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 (1000, 1200), the first supporting part of the first holding frame (1000, 1200) supports the third supporting part of the second holding frame (1002, 1202), and the second supporting part of the first holding frame (1000, 1200) supports the fourth supporting part of the second holding frame (1002, 1202); characterized in that the first holding frame (1000, 1200) 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 (1002, 1202) 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 (1000, 1200) 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.