A lightning arrester comprises a housing; a mainbody partially mounted in the housing; an encapsulation cap mounted at a first end of the housing; and an elastic apparatus compressed between the encapsulation cap and the mainbody. In the lightning arrester, the encapsulation cap comprises a circular base mounted at the first end of the housing and a mounting portion formed at a substantial center of the base. A first end of the elastic apparatus is mounted in the mounting portion, and a second thereof is abutted against the mainbody. In the lightning arrester, a reliable electrical connection may be arrived. By the pressure relief apparatus, electronic devices and accessories of the lightning arrester may be prevented from being damaged by escaped substance generated during the lightning arrester exploding.