The purpose of this paper is to study prehomomorphisms on regular *-semigroups which were firstly introduced in [5] . Firstly, we shall give a generalization of the natural order on a regular *-semigroup. Secondly, we shall discuss prehomomorphisms on regular *-semigroups. Finally, we shall obtain a generalization of a Preston-Vagner's representation to a regular *-sermgroup.