A slide rail assembly comprising: a supporting frame; a first rail movable relative to the supporting frame; a second rail movable relative to the first rail; a third rail movable relative to the second rail, and the second rail being movably mounted between the first rail and the third rail; a blocking structure arranged on the supporting frame; a positioning structure arranged on the supporting frame; a blocking feature arranged on the first rail; a positioning feature arranged on the first rail; a first working member movably mounted on the first rail and switchable between a first state and a second state relative to the first rail; and a second working member movably mounted on the first rail and switchable between a third state and a fourth state relative to the first rail; characterized in that: wherein when the first rail is located at a first predetermined position relative to the supporting frame, the blocking structure blocks the first working member in the first state for preventing the first rail from moving along a retracting direction from the first predetermined position; wherein when the first rail is located at a second predetermined position relative to the supporting frame, the second working member in the third state engages with the positioning structure for preventing the first rail from moving along an opening direction from the second predetermined position; wherein when the first rail is located at the second predetermined position relative to the supporting frame and the third rail is located at a retracted position relative to the first rail, the third rail is configured to support the second working member, such that the second working member is retained in the fourth state and does not engage with the positioning structure for allowing the first rail to move along the opening direction from the second predetermined position. a supporting frame; a first rail movable relative to the supporting frame; a second rail movable relative to the first rail; a third rail movable relative to the second rail, and the second rail being movably mounted between the first rail and the third rail; a blocking structure arranged on the supporting frame; a positioning structure arranged on the supporting frame; a blocking feature arranged on the first rail; a positioning feature arranged on the first rail; a first working member movably mounted on the first rail and switchable between a first state and a second state relative to the first rail; and a second working member movably mounted on the first rail and switchable between a third state and a fourth state relative to the first rail; characterized in that: wherein when the first rail is located at a first predetermined position relative to the supporting frame, the blocking structure blocks the first working member in the first state for preventing the first rail from moving along a retracting direction from the first predetermined position; wherein when the first rail is located at a second predetermined position relative to the supporting frame, the second working member in the third state engages with the positioning structure for preventing the first rail from moving along an opening direction from the second predetermined position; wherein when the first rail is located at the second predetermined position relative to the supporting frame and the third rail is located at a retracted position relative to the first rail, the third rail is configured to support the second working member, such that the second working member is retained in the fourth state and does not engage with the positioning structure for allowing the first rail to move along the opening direction from the second predetermined position. wherein when the first rail is located at a first predetermined position relative to the supporting frame, the blocking structure blocks the first working member in the first state for preventing the first rail from moving along a retracting direction from the first predetermined position; wherein when the first rail is located at a second predetermined position relative to the supporting frame, the second working member in the third state engages with the positioning structure for preventing the first rail from moving along an opening direction from the second predetermined position; wherein when the first rail is located at the second predetermined position relative to the supporting frame and the third rail is located at a retracted position relative to the first rail, the third rail is configured to support the second working member, such that the second working member is retained in the fourth state and does not engage with the positioning structure for allowing the first rail to move along the opening direction from the second predetermined position.