A slide rail assembly includes a first rail including a blocking member and a positioning member, a second rail including a predetermined feature, a working member and an operation member. When the second rail is at a first extending position, the blocking member is in a blocking state capable of blocking the working member so as to prevent the second rail from displacing along a retracting direction. The operation member is capable of being operated to drive the blocking member to leave the blocking state so as to allow the second rail to displace along the retracting direction. When the second rail is displaced from the first extending position to a second extending position along the retracting direction, the second rail is engaged with the positioning member through the predetermined feature so as to prevent the second rail from leaving the second extending position.