A slide rail assembly, comprising: a first rail comprising a positioning member and a blocking member ; a second rail capable of displacing relative to the first rail , the second rail comprising a predetermined feature ; and an operation member ; wherein when the second rail is displaced relative to the first rail from a first extending position (E1) to a second extending position (E2) along a retracting direction (D2), the second rail is engaged with the positioning member through the predetermined feature so as to prevent the second rail from leaving the second extending position (E2); wherein the positioning member is driven through the operation member being operably moved from a second operation position (P2) to a first operation position (P1), such that the predetermined feature is no longer engaged with the positioning member so as to allow the second rail to leave the second extending position (E2); wherein when the second rail is at the first extending position (E1) relative to the first rail , the blocking member is for blocking the second rail so as to prevent the second rail from displacing from the first extending position (E1) along the retracting direction (D2); wherein the blocking member is driven through the operation member being operably moved from the first operation position (P1) to the second operation position (P2), such that the blocking member is incapable of blocking the second rail so as to allow the second rail to displace from the first extending position (E1) along the retracting direction (D2); wherein each of the blocking member and positioning member comprises an elastic material; characterize d in that: wherein each of the blocking member and positioning member is an elastic sheet structure, and protrudes from a longitudinal wall of the first rail and faces toward the second rail . a first rail comprising a positioning member and a blocking member ; a second rail capable of displacing relative to the first rail , the second rail comprising a predetermined feature ; and an operation member ; wherein when the second rail is displaced relative to the first rail from a first extending position (E1) to a second extending position (E2) along a retracting direction (D2), the second rail is engaged with the positioning member through the predetermined feature so as to prevent the second rail from leaving the second extending position (E2); wherein the positioning member is driven through the operation member being operably moved from a second operation position (P2) to a first operation position (P1), such that the predetermined feature is no longer engaged with the positioning member so as to allow the second rail to leave the second extending position (E2); wherein when the second rail is at the first extending position (E1) relative to the first rail , the blocking member is for blocking the second rail so as to prevent the second rail from displacing from the first extending position (E1) along the retracting direction (D2); wherein the blocking member is driven through the operation member being operably moved from the first operation position (P1) to the second operation position (P2), such that the blocking member is incapable of blocking the second rail so as to allow the second rail to displace from the first extending position (E1) along the retracting direction (D2); wherein each of the blocking member and positioning member comprises an elastic material; characterize d in that: wherein each of the blocking member and positioning member is an elastic sheet structure, and protrudes from a longitudinal wall of the first rail and faces toward the second rail . <EOS>