Abstract: A positioning device for adjusting a horizontal position of a window frame is disclosed herein, which includes a tube-shaped seat having a chamber defined therein and a limit slot formed on a side wall thereof; a lifting tube, in which an end of the lifting tube is received in the chamber of the seat, a screw is inserted through the limit slot and screwed into a fixing hole on a side wall of the lifting tube, whereby the lifting tube can be fastened on the seat, and a portion of the lifting tube is exposed from a top of the seat; an upper board mounted on the other end of the lifting tube; and an elastic member sleeved into the lifting tube and having both ends respectively pressed against the seat and the upper board.