A slide rail assembly (20, 200, 400) comprising: a first rail (22, 212, 401) comprising a first end portion and a second end portion that are opposite to each other; a second rail (24, 210, 402) longitudinally movable relative to the first rail (22, 212, 401); a third rail (26, 214, 406) longitudinally movable relative to the second rail (24, 210, 402); a first supporting device (28, 412) exceeding the first end portion of the first rail (22, 212, 401) for a predetermined longitudinal distance, the first supporting device (28, 412) comprising a reinforcement member (58, 414) and a first bracket (60, 202, 422), the reinforcement member (58, 414) being connected to the first rail (22, 212, 401), the reinforcement member (58, 414) exceeding the first end portion of the first rail (22, 212, 401) for the predetermined longitudinal distance, and the first bracket (60, 202, 422) being connected to the reinforcement member (58, 414); and at least one supporting member (30, 206, 410); further characterized by an auxiliary member (76, 208, 403) connected to the second rail (24, 210, 402), wherein the at least one supporting member (30, 206, 410) is rotatably mounted on the auxiliary member (76, 208, 403), the second rail (24, 210, 402) comprises a first end portion (24a, 402a) and a second end portion that are opposite to each other, and the auxiliary member (76, 208, 403) is connected to the first end portion (24a, 402a) of the second rail (24, 210, 402) adjacent thereto, the second rail (24, 210, 402) is supported and contacted by one of the reinforcement member (58, 414) and the first bracket (60, 202, 422) through the at least one supporting member (30, 206, 410); wherein the at least one supporting member (30, 206, 410) is configured to be supported by and contacted along a first portion (64a, 415a) of the reinforcement member (58, 414) through an arced contour of the at least one supporting member (30, 206, 410) and a linear section of the first portion (64a, 415a) of the reinforcement member (58, 414) being contacted with each other, or be supported by and contacted along an extending portion of the first bracket longitudinally arranged through the arced contour of the at least one supporting member (30, 206, 410) and a linear section of the extending portion of the first bracket being contacted with each other when the second rail (24, 210, 402) is longitudinally moved relative to the first rail (22, 212, 401) from a retracted position to an extending position in an opening direction and when the second rail (24, 210, 402) is longitudinally moved relative to the first rail (22, 212, 401) from the extending position to the retracted position in a retracting direction. a first rail (22, 212, 401) comprising a first end portion and a second end portion that are opposite to each other; a second rail (24, 210, 402) longitudinally movable relative to the first rail (22, 212, 401); a third rail (26, 214, 406) longitudinally movable relative to the second rail (24, 210, 402); a first supporting device (28, 412) exceeding the first end portion of the first rail (22, 212, 401) for a predetermined longitudinal distance, the first supporting device (28, 412) comprising a reinforcement member (58, 414) and a first bracket (60, 202, 422), the reinforcement member (58, 414) being connected to the first rail (22, 212, 401), the reinforcement member (58, 414) exceeding the first end portion of the first rail (22, 212, 401) for the predetermined longitudinal distance, and the first bracket (60, 202, 422) being connected to the reinforcement member (58, 414); and at least one supporting member (30, 206, 410); further characterized by an auxiliary member (76, 208, 403) connected to the second rail (24, 210, 402), wherein the at least one supporting member (30, 206, 410) is rotatably mounted on the auxiliary member (76, 208, 403), the second rail (24, 210, 402) comprises a first end portion (24a, 402a) and a second end portion that are opposite to each other, and the auxiliary member (76, 208, 403) is connected to the first end portion (24a, 402a) of the second rail (24, 210, 402) adjacent thereto, the second rail (24, 210, 402) is supported and contacted by one of the reinforcement member (58, 414) and the first bracket (60, 202, 422) through the at least one supporting member (30, 206, 410); wherein the at least one supporting member (30, 206, 410) is configured to be supported by and contacted along a first portion (64a, 415a) of the reinforcement member (58, 414) through an arced contour of the at least one supporting member (30, 206, 410) and a linear section of the first portion (64a, 415a) of the reinforcement member (58, 414) being contacted with each other, or be supported by and contacted along an extending portion of the first bracket longitudinally arranged through the arced contour of the at least one supporting member (30, 206, 410) and a linear section of the extending portion of the first bracket being contacted with each other when the second rail (24, 210, 402) is longitudinally moved relative to the first rail (22, 212, 401) from a retracted position to an extending position in an opening direction and when the second rail (24, 210, 402) is longitudinally moved relative to the first rail (22, 212, 401) from the extending position to the retracted position in a retracting direction.