A slide rail assembly includes a first rail, a second rail, a third rail, and at least one supporting structure. The second rail is movable with respect to the first rail. The third rail is mounted between the first rail and the second rail. The at least one supporting structure is disposed at a position relative to the first rail. When the second rail is at a predetermined position relative to the first rail, the third rail supports a portion of the second rail, and the at least one supporting structure supports the remaining portion of the second rail.