A container cap assembly includes an inner cap coupled to an inner surface and an upper end of a container neck and an outer cap maintaining the coupled state of the inner cap, thereby keeping the inside of a container sealed. The container cap assembly includes an inner cap including an outer wall portion corresponding to an inner surface of a neck of a container and a flange portion extending outward from an upper end of the outer wall portion to correspond to an upper end of the neck. An outer cap has a ceiling covering an upper portion of the inner cap and a side wall portion covering an outer circumferential surface of the neck, the ceiling and the side wall portion being integrally formed. The inner circumferential surface of the side wall portion has female threads corresponding to male threads on the outer circumferential surface of the neck.