A two-way retainer for a slide track assembly comprises a retaining mechanism mounted on a first slide track, and a stop member mounted on a second slide track. The retaining mechanism is consisted of a pair of retaining arms and an elastic member. The retaining arms are provided with a pair of oppositely inclined portions and a pair of engaging portions. The stop member is provided with a protrusion adapted to interact with the oppositely inclined portions and the engaging portions of the retaining arms. When the first slide track is moved to a predetermined position with respect to the second slide track, the protrusion of the stop member may pass through one of the inclined portions of the retaining arms. Thus the protrusion is confined within the two engaging portions of the retaining arms to thereby retain the first slide track in a two-way direction of the second slide track.