A slide rail assembly includes a first rail, a second rail and a positioning device. The first rail includes a first structure and a second structure. The second rail is movable relative to the first rail. The positioning device is arranged to the second rail and includes an elastic member and a positioning member. The elastic member provides an elastic force to the positioning member. When the second rail is moved relative to the first rail from a first position to a second position, the positioning member is moved to an engaging position through the elastic force and abuts against the first structure. When the second rail is moved relative to the first rail from the second position to a third position, the positioning member is moved from the engaging position to a disengaging position and no longer abuts against the first structure by guidance of the second structure.