A slide rail assembly, comprising: a first rail defining a longitudinal channel; the first rail having an upper wall, a lower wall, and a sidewall extending between the upper wall and the lower wall, wherein the upper wall, the lower wall, and the sidewall jointly define the longitudinal channel, and the sidewall has an opening; a blocking member (34, 204) attached to the first rail; a second rail movably connected to the first rail and displaceable to an extended position relative to the first rail in the longitudinal channel so as to be blocked by the blocking member (34, 204); and an operating member (36, 200) movably connected to the first rail and configured to operate the blocking member (34, 204) and thereby allow the second rail to be retracted from the extended position relative to the first rail characterized in that the blocking member is an elastic plate and has a first portion, a second portion, a main body portion, and an auxiliary portion; wherein the first portion is configured to be connected to the sidewall of the first rail, the second portion is distant from the first portion, the main body portion and the auxiliary portion are located between the first portion and the second portion; and wherein the auxiliary portion is raised transversely from the main body portion and extends towards the opening of the first rail; wherein the auxiliary portion includes a guide section and a stop wall, the stop wall (50, 208) corresponding to the opening of the first rail; wherein the slide rail assembly further comprises a positioning member, the positioning member being arranged at the second rail and has a portion (84, 206) to be guided by the guide section of the blocking member until being blocked by the stop wall (50, 208) of the blocking member (34, 204) when the second rail is displaced to the extended position; and wherein the portion (84, 206) of the positioning member is released from the stop wall (50, 208) of the blocking member (34, 204) when the blocking member (34, 204) is operated by the operating member (36, 200) so that the second rail is allowed to be retracted from the extended position relative to the first rail. a first rail defining a longitudinal channel; the first rail having an upper wall, a lower wall, and a sidewall extending between the upper wall and the lower wall, wherein the upper wall, the lower wall, and the sidewall jointly define the longitudinal channel, and the sidewall has an opening; a blocking member (34, 204) attached to the first rail; a second rail movably connected to the first rail and displaceable to an extended position relative to the first rail in the longitudinal channel so as to be blocked by the blocking member (34, 204); and an operating member (36, 200) movably connected to the first rail and configured to operate the blocking member (34, 204) and thereby allow the second rail to be retracted from the extended position relative to the first rail characterized in that the blocking member is an elastic plate and has a first portion, a second portion, a main body portion, and an auxiliary portion; wherein the first portion is configured to be connected to the sidewall of the first rail, the second portion is distant from the first portion, the main body portion and the auxiliary portion are located between the first portion and the second portion; and wherein the auxiliary portion is raised transversely from the main body portion and extends towards the opening of the first rail; wherein the auxiliary portion includes a guide section and a stop wall, the stop wall (50, 208) corresponding to the opening of the first rail; wherein the slide rail assembly further comprises a positioning member, the positioning member being arranged at the second rail and has a portion (84, 206) to be guided by the guide section of the blocking member until being blocked by the stop wall (50, 208) of the blocking member (34, 204) when the second rail is displaced to the extended position; and wherein the portion (84, 206) of the positioning member is released from the stop wall (50, 208) of the blocking member (34, 204) when the blocking member (34, 204) is operated by the operating member (36, 200) so that the second rail is allowed to be retracted from the extended position relative to the first rail.