A slide rail assembly includes a first rail, a second rail slidably received in the first rail, a mounting bracket fixed to the second rail, a positioning member movably mounted to the mounting bracket, and a releasing member slidably mounted to the second rail. The first rail includes a holding portion. The positioning member engages with the holding portion to prevent the second rail from sliding into or out of the first rail. By sliding the releasing member, the releasing member drives the positioning member to disengage from the holding portion of the first rail, thereby enabling the second rail to slide into or out of the first rail.