Abstract: A lid assembly includes a lid body having a periphery containing a liquid discharge slot and an air vent arranged diametrically opposite to each other, and a center containing a passage located between the liquid discharge slot and the air vent, a rotary cap rotatably mounted on the top of the lid body and including a drive post extending downward from the bottom thereof, and extending through the passage, a control device mounted on the bottom of the lid body and secured to the drive post to rotate therewith. In such a manner, the control device can be rotated by the drive post to move between a first position where the liquid discharge slot and the air vent are closed by the control device, and a second position where the liquid discharge slot and the air vent are detached from and opened by the control device.