Abstract - In the first part, via the transposition of the theorems of Birkhoff, Chaunier-Lygeros and Lygeros-Mizony on Groups to P-Hypergroups, we explicit some relations between posets and hypergroups. In the second part, we generalize Vougiouklis results on hypergroups of order 2 and we enumerate and classify all the Hypergroups of order 3.