To provide an agent for removing scale, by means of which a solid scale adhered to piping and tanks in a toilet room can be removed simply and easily in a short time, particularly by a mechanic for aircraft and the like, without dismantling piping, and further which does not corrode or hydrogen-embrittle the metallic materials of piping, tanks and vehicles, and a method for removing scale.

There are provided an agent for removing scale adhered to piping and tanks in a toilet room, which is a composition comprising a chelating agent, a silicate and water as essential components, the composition exhibiting alkaline, and a removing method using the same.