An air vent for liquid containers such as baby bottles, flasks, or the like, for containing any liquid easily poured through an upper spout such as a nipple or a hard plastic spout or even a metal spout. The container includes an air vent defined by a system based on the principle of communicating vessels acted upon by equal air pressures, defined by a duct of an adequate diameter placed in a vertical or oblique manner, whose lower end is placed inside and in the bottom of the container, while the upper end defines an external air inlet that is open to external air. The duct communicates with the main internal space in the bottom of the container, such that when the container is sufficiently tilted, the liquid inside the duct may go to the bottom of the container, enabling a free flow of external air to the bottom of the container, without passing through the liquid, thus preventing the formation of a vacuum in the bottom of the container, before even this same liquid be discharged or sucked from the container.
