A slide rail assembly, comprising: a first rail; a second rail movable relative to the first rail; a blocking structure mounted to the first rail;a locking member movably mounted to the second rail and configured to abut against the blocking structure, in order to prevent the second rail from being moved relative to the first rail from a retracted position along an opening direction; an operating member configured to be operated to disengage the locking member from the blocking structure for allowing the second rail to be moved relative to the first rail from the retracted position along the opening direction; a third rail; a contact member; a synchronization member; and characterized by: a fastening member movably mounted to the third rail; wherein the third rail is movably mounted between the first rail and the second rail, the contact member is mounted to the first rail, the synchronization member is movably mounted to the third rail; when the second rail is moved from the retracted position along the opening direction, the third rail is synchronously moved with the second rail relative to the first rail along the opening direction through the synchronization member; and when the second rail and the third rail are moved to a first predetermined position, the third rail is no longer synchronously moved with the second rail due to interaction between the synchronization member and the contact member; wherein when the third rail is moved from the first predetermined position to a second predetermined position along the opening direction, the fastening member is configured to be fastened to the contact member, in order to prevent the third rail from being retracted relative to the first rail. a first rail; a second rail movable relative to the first rail; a blocking structure mounted to the first rail;a locking member movably mounted to the second rail and configured to abut against the blocking structure, in order to prevent the second rail from being moved relative to the first rail from a retracted position along an opening direction; an operating member configured to be operated to disengage the locking member from the blocking structure for allowing the second rail to be moved relative to the first rail from the retracted position along the opening direction; a third rail; a contact member; a synchronization member; and characterized by: a fastening member movably mounted to the third rail; wherein the third rail is movably mounted between the first rail and the second rail, the contact member is mounted to the first rail, the synchronization member is movably mounted to the third rail; when the second rail is moved from the retracted position along the opening direction, the third rail is synchronously moved with the second rail relative to the first rail along the opening direction through the synchronization member; and when the second rail and the third rail are moved to a first predetermined position, the third rail is no longer synchronously moved with the second rail due to interaction between the synchronization member and the contact member; wherein when the third rail is moved from the first predetermined position to a second predetermined position along the opening direction, the fastening member is configured to be fastened to the contact member, in order to prevent the third rail from being retracted relative to the first rail. a fastening member movably mounted to the third rail; wherein the third rail is movably mounted between the first rail and the second rail, the contact member is mounted to the first rail, the synchronization member is movably mounted to the third rail; when the second rail is moved from the retracted position along the opening direction, the third rail is synchronously moved with the second rail relative to the first rail along the opening direction through the synchronization member; and when the second rail and the third rail are moved to a first predetermined position, the third rail is no longer synchronously moved with the second rail due to interaction between the synchronization member and the contact member; wherein when the third rail is moved from the first predetermined position to a second predetermined position along the opening direction, the fastening member is configured to be fastened to the contact member, in order to prevent the third rail from being retracted relative to the first rail.