Seal cap

A seal cap includes a main body, a retaining cover and a fastening ring. The main body has a slab shape and is flexible. The main body includes a press collar extending upward from the main body. The press collar has a connecting portion therein. The retaining cover covers the main body, and includes an annular inner wall, an outer covering body, a trough and a coupling portion. The outer covering body covers the annular inner wall and has at least one press opening. The trough is formed between the outer covering body and the annular inner wall, and faces downward. The trough communicates with the at least one press opening. The press collar is inserted located in the trough. The coupling portion encircles the outer covering body, and is located above the engaging portion. The fastening ring is located at an outer side of the connecting portion of the main body, so that the connecting portion is tightly connected to the annular inner wall of the retaining cover. When in use, the seal cap of the present invention is coupled to the opening of a container. The top of the container leans against the coupling portion, and the circumferential wall is against the container to seal the container.