The present invention relates to a bottle cap. Conventional bottle caps include a one-touch cap or a rotary cap which is correspondingly shaped to the spiral opening of the bottle. The rotary cap is capable of sealing the bottle tightly but can be easily lost. The one-touch cap will not be lost because the cap is held in the bottle even when it is opened but the seal is not tight. Accordingly, the objective of the present invention is to provide a bottle cap which seals the bottle tightly and eliminates the risk of the bottle cap falling off. Therefore, the disclosed invention characterizes the mouth of the bottle as a hinged cap.