An automatic return device for a glass door, the device comprising: a hydraulic hinge assembly, comprising: a first fixing plate; a first base, being fixedly connected to the first fixing plate and defining therein an oil storage area extending transversely and a first axial hole vertically communicated with the oil storage area; a piston unit, having a piston seat that is received in the oil storage area in a transversely movable manner, wherein the piston seat has a guide groove that extends vertically and has two racks flanking the guide groove; a first drive axle, having a first shaft and a guide wheel attached to the first shaft, the first shaft being rotatably received in the first axial hole and have two ends thereof exposed outside the first axial hole, the guide wheel being located in the guide groove of the piston seat, the guide wheel having a tooth portion for selectively engaging with the two racks, so that the piston seat is guided by the guide wheel and presses oil in the oil storage area; a first grip unit, gripping the glass door and being connected to two ends of the first shaft so as to pivot with the first shaft synchronously; and a leaf positioning assembly, comprising: a second fixing plate; a second base, being fixedly connected to the second fixing plate and defining therein a transversely extending receiving area and a second axial hole vertically communicated with the receiving area; a slide seat unit, comprises a slide seat, a first ball, and a second spring, wherein the slide seat is set in the receiving area in a transversely movable manner, and the second spring is set in the receiving area to abut against one end of the slide seat whose opposite end is provided with a depression for receiving the first ball; a second drive axle, having a second shaft and a cam attached to the second shaft, the second shaft being rotatably received in the second axial hole and having two ends thereof exposed outside the second axial hole, the cam having a front end and two lateral ends connected to the front end, each of the front end and the two lateral ends having a pit for the first ball to selectively lean against one of the pits; and a second grip unit, gripping the glass door and being connected to two ends of the second shaft so as to pivot with the second shaft synchronously. a first fixing plate; a first base, being fixedly connected to the first fixing plate and defining therein an oil storage area extending transversely and a first axial hole vertically communicated with the oil storage area; a piston unit, having a piston seat that is received in the oil storage area in a transversely movable manner, wherein the piston seat has a guide groove that extends vertically and has two racks flanking the guide groove; a first drive axle, having a first shaft and a guide wheel attached to the first shaft, the first shaft being rotatably received in the first axial hole and have two ends thereof exposed outside the first axial hole, the guide wheel being located in the guide groove of the piston seat, the guide wheel having a tooth portion for selectively engaging with the two racks, so that the piston seat is guided by the guide wheel and presses oil in the oil storage area; a first grip unit, gripping the glass door and being connected to two ends of the first shaft so as to pivot with the first shaft synchronously; and a leaf positioning assembly, comprising: a second fixing plate; a second base, being fixedly connected to the second fixing plate and defining therein a transversely extending receiving area and a second axial hole vertically communicated with the receiving area; a slide seat unit, comprises a slide seat, a first ball, and a second spring, wherein the slide seat is set in the receiving area in a transversely movable manner, and the second spring is set in the receiving area to abut against one end of the slide seat whose opposite end is provided with a depression for receiving the first ball; a second drive axle, having a second shaft and a cam attached to the second shaft, the second shaft being rotatably received in the second axial hole and having two ends thereof exposed outside the second axial hole, the cam having a front end and two lateral ends connected to the front end, each of the front end and the two lateral ends having a pit for the first ball to selectively lean against one of the pits; and a second grip unit, gripping the glass door and being connected to two ends of the second shaft so as to pivot with the second shaft synchronously. a second fixing plate; a second base, being fixedly connected to the second fixing plate and defining therein a transversely extending receiving area and a second axial hole vertically communicated with the receiving area; a slide seat unit, comprises a slide seat, a first ball, and a second spring, wherein the slide seat is set in the receiving area in a transversely movable manner, and the second spring is set in the receiving area to abut against one end of the slide seat whose opposite end is provided with a depression for receiving the first ball; a second drive axle, having a second shaft and a cam attached to the second shaft, the second shaft being rotatably received in the second axial hole and having two ends thereof exposed outside the second axial hole, the cam having a front end and two lateral ends connected to the front end, each of the front end and the two lateral ends having a pit for the first ball to selectively lean against one of the pits; and a second grip unit, gripping the glass door and being connected to two ends of the second shaft so as to pivot with the second shaft synchronously.