Abstract: A leakage preventive device is provided for use on a milk bottle or the like to help prevent the milk contained in the bottle from leaking out when the bottle falls aside or is subjected to violent shaking. The leakage preventive device comprises: a mounting device having a cylindrical body formed with a hollowed inside serving as a passage for the liquid contained in the bottle; and an elastic valve member mounted on the mounting device. The elastic valve member is formed with a thick outer wall, which can be fitted tightly to the outer wall of the cylindrical body of the mounting device, and a substantially U-shaped inner ring, which can be linked to the outer wall. The U-shaped inner ring is made from an elastic material, allowing the U-shaped inner ring to urge forcibly against the inner wall of the cylindrical body when the teat is not being sucked; the U-shaped inner ring having an open end to define a chamber connected to the teat.