A bottle stopper includes a cover body, a shaft rod and a rotatable member. The shaft rod is fixed inside the cover body and the rotatable member is secured on the cover body by means of an insert pin, which leans on two opposite oblique faces of the projecting base of the cover body. When the rotatable member is turned clockwise, the insert pin will be actuated to slide upward along the oblique faces of the projecting base and drive the shaft rod to move upward and squeeze a soft clogging member to expand outward and clog the bottle mouth of a bottle. The bottle stopper of this invention can be closely clogged in the bottle mouth, and its shaft rod and soft clogging member are hidden in the cover body, meeting sanitation, convenient in use and able to be placed horizontally for facilitating storing.