A slide rail assembly , comprising: a first rail comprising a first wall , a second wall and a longitudinal wall connected between the first wall and the second wall , the first wall , the second wall and the longitudinal wall cooperatively defining a channel , the channel having a channel opening ; a second rail ; and characterized by : a guiding structure disposed adjacent to the channel opening of the channel and for guiding the second rail to be mounted into the channel via the channel opening ; wherein the guiding structure comprises a first guiding portion and a second guiding portion , the first guiding portion is disposed adjacent to one of the first wall and the second wall , the second guiding portion is disposed adjacent to the other one of the first wall and the second wall ; wherein the guiding structure further comprises a third guiding portion , and the third guiding portion is disposed adjacent to the longitudinal wall , the third guiding portion comprises a first inclined surface , a second inclined surface and a third inclined surface , the first inclined surface corresponds to a side wall of the second rail , the second inclined surface and the third inclined surface are disposed on opposite sides of the first inclined surface , the second inclined surface corresponds to a third wall of the second rail , the third inclined surface corresponds to a fourth wall of the second rail . a first rail comprising a first wall , a second wall and a longitudinal wall connected between the first wall and the second wall , the first wall , the second wall and the longitudinal wall cooperatively defining a channel , the channel having a channel opening ; a second rail ; and characterized by : a guiding structure disposed adjacent to the channel opening of the channel and for guiding the second rail to be mounted into the channel via the channel opening ; wherein the guiding structure comprises a first guiding portion and a second guiding portion , the first guiding portion is disposed adjacent to one of the first wall and the second wall , the second guiding portion is disposed adjacent to the other one of the first wall and the second wall ; wherein the guiding structure further comprises a third guiding portion , and the third guiding portion is disposed adjacent to the longitudinal wall , the third guiding portion comprises a first inclined surface , a second inclined surface and a third inclined surface , the first inclined surface corresponds to a side wall of the second rail , the second inclined surface and the third inclined surface are disposed on opposite sides of the first inclined surface , the second inclined surface corresponds to a third wall of the second rail , the third inclined surface corresponds to a fourth wall of the second rail . a guiding structure disposed adjacent to the channel opening of the channel and for guiding the second rail to be mounted into the channel via the channel opening ; wherein the guiding structure comprises a first guiding portion and a second guiding portion , the first guiding portion is disposed adjacent to one of the first wall and the second wall , the second guiding portion is disposed adjacent to the other one of the first wall and the second wall ; wherein the guiding structure further comprises a third guiding portion , and the third guiding portion is disposed adjacent to the longitudinal wall , the third guiding portion comprises a first inclined surface , a second inclined surface and a third inclined surface , the first inclined surface corresponds to a side wall of the second rail , the second inclined surface and the third inclined surface are disposed on opposite sides of the first inclined surface , the second inclined surface corresponds to a third wall of the second rail , the third inclined surface corresponds to a fourth wall of the second rail . <EOS>