A positioning apparatus for seat headrest posts in vehicle is provided, including a retractable rod, two clamping units and a connection joint unit; wherein the retractable rod having an extendible rod able to extend and retract; a locking assembly being disposed on the outer surface of the retractable rod; the locking assembly being able to fasten the position after lateral adjustment of the retractable rod; the two clamping units being disposed on the retractable rod for clamping onto the posts of seat headrest; the connection joint unit being disposed to the end of the extendible rod for engaging an object to be mounted here. As such, when an electronic device, such as, tablet or thin screen display is mounted to the connection joint unit, the position of the electronic device can be adjusted by adjusting the length of the extendible rod for convenient viewing.