A slide rail assembly, comprising: a first rail; a second rail movable relative to the first rail; a third rail movably mounted between the first rail and the second rail, wherein the third rail has a first elongated hole and a second elongated hole; characterized by: a contact member mounted to the first rail; a synchronization member pivoted to the third rail by a first shaft member and configured to be deflected between the first rail and the second rail through the first elongated hole; and a fastening member pivoted to the third rail by a second shaft member and configured to be deflected between the first rail and the second rail through the second elongated hole; wherein when the second rail is moved from a retracted position along an 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 along a retracted direction. a first rail; a second rail movable relative to the first rail; a third rail movably mounted between the first rail and the second rail, wherein the third rail has a first elongated hole and a second elongated hole; characterized by: a contact member mounted to the first rail; a synchronization member pivoted to the third rail by a first shaft member and configured to be deflected between the first rail and the second rail through the first elongated hole; and a fastening member pivoted to the third rail by a second shaft member and configured to be deflected between the first rail and the second rail through the second elongated hole; wherein when the second rail is moved from a retracted position along an 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 along a retracted direction. a contact member mounted to the first rail; a synchronization member pivoted to the third rail by a first shaft member and configured to be deflected between the first rail and the second rail through the first elongated hole; and a fastening member pivoted to the third rail by a second shaft member and configured to be deflected between the first rail and the second rail through the second elongated hole; wherein when the second rail is moved from a retracted position along an 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 along a retracted direction.