Ali Ghaffari - Semnan University
Mohammad Bagher Sahabi - Payame Noor University

Let K be a locally compact hypergroup with left Haar measure and let L^۱(K) be the complex Lebesgue space associated with it. Let L^\infty(K) be the dual of L^۱(K). The purpose of this paper is to present some necessary and sufficient conditions for L^\infty(K)^* to have a topologically left invariant mean. Some characterizations of amenable hypergroups are given.