Abstract. In this paper, we study α-completely positive maps between locally C * -algebras. As a generalization of a completely positive map, an α-completely positive map produces a Krein space with indefinite metric, which is useful for the study of massless or gauge fields. We construct a KSGNS type representation associated to an α-completely positive map of a locally C * -algebra on a Krein locally C * -module. Using this construction, we establish the Radon-Nikodým type theorem for α-completely positive maps on locally C * -algebras. As an application, we study an extremal problem in the partially ordered cone of α-completely positive maps on a locally C * -algebra.