Abstract: A track assembly includes a track member, which has two parallel sliding grooves arranged in parallel at two sides and two locating holes spaced between the sliding grooves, a sliding member, which has two sliding rails respectively coupled to the sliding grooves of the track member and two locating holes spaced between the sliding rails, and two torsional springs arranged in the same direction on said track member and respectively connected between the locating holes of the track member and the locating holes of the sliding member such that the torsional springs automatically pushes the sliding rail to the open or close position when the user pushes the sliding rail to the midway toward the open or close position.