A slide rail assembly, comprising: a first rail; a second rail displaceable with respect to the first rail from a first position to a second position; and a third rail displaceable with respect to the second rail; that the slide rail assembly further comprises a locking member switchable between a first state (S 1) and a second state, wherein the locking member is configured to prevent the second rail from displacement with respect to the first rail from the second position toward the first position when in the first state; and that the slide rail assembly further comprises an operating member configured to be manually operated in order for a driving portion of the operating member to drive a linking feature of the locking member and thereby switch the locking member from the first state to the second state, in which the second rail is allowed to be displaced with respect to the first rail from the second position toward the first position; wherein the locking member is movably mounted on the second rail, and there is an elastic member for applying an elastic force to the locking member and thereby keeping the locking member in the first state; wherein the first rail includes a guiding portion and a first blocking feature, the locking member includes an engaging portion and a contact portion, and there is a pivotally connecting element disposed between the engaging portion and the contact portion to pivotally connect the locking member to the second rail; and wherein when the locking member is in the first state, the engaging portion of the locking member is lockable to the first blocking feature; characterized in wherein when the locking member is in the first state, the third rail is able to drive the second rail through the contact portion of the locking member to bring about simultaneous displacement of the second rail and the third rail in a first direction; when the second rail reaches a predetermined position after the simultaneous displacement, the locking member comes into contact with the guiding portion of the first rail such that a force acts on the locking member and brings the locking member out of the first state (S 1), thereby terminating a simultaneous displacement relationship between the second rail and the third rail, with the elastic member storing an elastic force; and when the second rail reaches the second position after further displacement in the first direction, the locking member is switched back to the first state (S 1) in response to the elastic force of the elastic member such that the engaging portion of the locking member is locked to the first blocking feature of the first rail to prevent the second rail from displacement from the second position to the first position in a second direction. a first rail; a second rail displaceable with respect to the first rail from a first position to a second position; and a third rail displaceable with respect to the second rail; that the slide rail assembly further comprises a locking member switchable between a first state (S 1) and a second state, wherein the locking member is configured to prevent the second rail from displacement with respect to the first rail from the second position toward the first position when in the first state; and that the slide rail assembly further comprises an operating member configured to be manually operated in order for a driving portion of the operating member to drive a linking feature of the locking member and thereby switch the locking member from the first state to the second state, in which the second rail is allowed to be displaced with respect to the first rail from the second position toward the first position; wherein the locking member is movably mounted on the second rail, and there is an elastic member for applying an elastic force to the locking member and thereby keeping the locking member in the first state; wherein the first rail includes a guiding portion and a first blocking feature, the locking member includes an engaging portion and a contact portion, and there is a pivotally connecting element disposed between the engaging portion and the contact portion to pivotally connect the locking member to the second rail; and wherein when the locking member is in the first state, the engaging portion of the locking member is lockable to the first blocking feature; characterized in wherein when the locking member is in the first state, the third rail is able to drive the second rail through the contact portion of the locking member to bring about simultaneous displacement of the second rail and the third rail in a first direction; when the second rail reaches a predetermined position after the simultaneous displacement, the locking member comes into contact with the guiding portion of the first rail such that a force acts on the locking member and brings the locking member out of the first state (S 1), thereby terminating a simultaneous displacement relationship between the second rail and the third rail, with the elastic member storing an elastic force; and when the second rail reaches the second position after further displacement in the first direction, the locking member is switched back to the first state (S 1) in response to the elastic force of the elastic member such that the engaging portion of the locking member is locked to the first blocking feature of the first rail to prevent the second rail from displacement from the second position to the first position in a second direction.