Disclosed is a seal structure of a high-pressure tank capable of properly securing seal efficiency. The seal structure of the high-pressure tank includes a plurality of seal members that have mutually different seal properties and that are installed between a ferrule of the high-pressure tank and a valve body attached to the ferrule. One of the plurality of seal members has low temperature resistance, and the other has high temperature resistance. A first seal member is an O-ring formed of butyl rubber or silicone. A second seal member is an O-ring formed of EPDM. Furthermore, the two O-rings are different in gas permeability from each other. This seal structure can be applied between the ferrule and the valve body, in addition, between the ferrule and a liner, between the ferrule and a shell, and between the valve body and the shell.