Abstract
The main task in this article is to give the necessary and sufficient conditions guarantees that the product of two positive definite functions defined on a hypergroup X is also positive definite on X. Also, we prove that a continuous function with compact support psi is negative definite if and only if exp(-t psi) is positive definite for each t > 0. Moreover, we will give some relations between the class of completely monotonic functions on a hypergroup and the set of tau- positive functions.