Abstract: A paper cap having an improved structure to prevent a skirt part from being deformed and the paper cap from being easily separated from a container is disclosed. The paper cap includes a circular plane part for covering an upper portion of a container and a skirt part extending downward from an edge of the plane part. The skirt part has a circumference groove fitted into a curling part of the paper cup and a ring-shaped reinforcing groove on which a plurality of uneven wrinkles are formed in a length direction and which is formed along the inner circumference surface at a position spaced apart from the circumference groove.