A headrest assembly for a chair (9) includes a headrest unit (3), two spaced-apart grip frame members (23) respectively connected to two opposite ends of the headrest unit (3), and two spaced-apart connection frame members (21) respectively connected to the grip frame members (23). The grip frame members (23) gradually extend away from each other from the headrest unit (3) to the connection framemembers (21), respectively. Each of the grip frame members (23) extends obliquely, rearwardly and downwardly from the headrest unit (3) in a manner of being oblique to a first vertical plane (81) that has opposite front and rear surfaces respectively facing front and rear sides of the chair (9).
