A slide rail assembly, comprising: a first rail including a first wall, a second wall, and a longitudinal wall connected between the first wall and the second wall of the first rail, wherein the first wall, the second wall, and the longitudinal wall of the first rail jointly define a channel; a blocking feature provided on the first rail at a position adjacent to the first wall of the first rail; and a second rail including a first wall, a second wall, and a longitudinal wall connected between the first wall and the second wall of the second rail; wherein the slide rail assembly further comprises a foolproof feature provided on the second rail at a position adjacent to the second wall of the second rail, characterized in that: the foolproof feature and the blocking feature are configured to work together to prevent the second rail from being mounted incorrectly into the channel of the first rail, wherein: the second rail is configured to be mounted back into the channel of the first rail in a retracting direction from outside the channel of the first rail, wherein while the second rail is being inserted into the channel of the first rail in the retracting direction from outside the channel of the first rail, with the first wall of the second rail being adjacent to the first wall of the first rail, the foolproof feature and the blocking feature do not block each other and therefore allow the second rail to be retracted with respect to the first rail; and in an erroneous mounting process, the second rail is turned through a predetermined angle with respect to the first rail and therefore cannot be mounted into the channel of the first rail in the retracting direction from outside the channel of the first rail, wherein while the second rail is being inserted into the channel of the first rail in the retracting direction from outside the channel of the first rail, with the first wall of the second rail being adjacent to the second wall of the first rail, the foolproof feature and the blocking feature of the first rail block each other, thus preventing the second rail from being retracted with respect to the first rail in the retracting direction, wherein the aforesaid predetermined angle is substantially 180 degrees. a first rail including a first wall, a second wall, and a longitudinal wall connected between the first wall and the second wall of the first rail, wherein the first wall, the second wall, and the longitudinal wall of the first rail jointly define a channel; a blocking feature provided on the first rail at a position adjacent to the first wall of the first rail; and a second rail including a first wall, a second wall, and a longitudinal wall connected between the first wall and the second wall of the second rail; wherein the slide rail assembly further comprises a foolproof feature provided on the second rail at a position adjacent to the second wall of the second rail, characterized in that: the foolproof feature and the blocking feature are configured to work together to prevent the second rail from being mounted incorrectly into the channel of the first rail, wherein: the second rail is configured to be mounted back into the channel of the first rail in a retracting direction from outside the channel of the first rail, wherein while the second rail is being inserted into the channel of the first rail in the retracting direction from outside the channel of the first rail, with the first wall of the second rail being adjacent to the first wall of the first rail, the foolproof feature and the blocking feature do not block each other and therefore allow the second rail to be retracted with respect to the first rail; and in an erroneous mounting process, the second rail is turned through a predetermined angle with respect to the first rail and therefore cannot be mounted into the channel of the first rail in the retracting direction from outside the channel of the first rail, wherein while the second rail is being inserted into the channel of the first rail in the retracting direction from outside the channel of the first rail, with the first wall of the second rail being adjacent to the second wall of the first rail, the foolproof feature and the blocking feature of the first rail block each other, thus preventing the second rail from being retracted with respect to the first rail in the retracting direction, wherein the aforesaid predetermined angle is substantially 180 degrees. in an erroneous mounting process, the second rail is turned through a predetermined angle with respect to the first rail and therefore cannot be mounted into the channel of the first rail in the retracting direction from outside the channel of the first rail, wherein while the second rail is being inserted into the channel of the first rail in the retracting direction from outside the channel of the first rail, with the first wall of the second rail being adjacent to the second wall of the first rail, the foolproof feature and the blocking feature of the first rail block each other, thus preventing the second rail from being retracted with respect to the first rail in the retracting direction, wherein the aforesaid predetermined angle is substantially 180 degrees.