This paper studies the algebraic structure of transposition hypergroups with idempotent identity. Their subhypergroups and their properties are examined. Right, left and double cosets are defined through symmetric subhypergroups and their properties are studied. Further- more, this paper examines the homomorphisms, the behaviour of attrac- tive and non-attractive elements through them, as well as the relation of their kernels and images to symmetric subhypergroups.