Abstract: Genetic diversity of six species of tilapia in Hainan Province was studied with twenty pairs of previously screened microsatellite primers to analyze the genetic variation and genetic relationships among these groups.The genetic parameters in different groups were also compared,which included allele number,efficient allele number,observation heterozygosity,expectation heterozygosity,Shannon's polymorphism index,average polymorphic information content,etc.A systematic cluster map of six tilapia groups was constructed using genetic distance.The results showed that the number of allele of the 6 groups was 68.The average allele number was 1.992 2~2.255 8.The average observed heterozygosity was 0.572 5~0.745 0.The average expected heterozygosity was 0.469 2~0.532 3.The Shannon's diversity index was 0.719 3~0.848 6.The polymorphic information content got 0.25 < PIC < 0.5.The highest genetic diversity of tilapia is Oreochromis mossambica,and the lowest is Oreochromis niloticus×O.aureus.The cluster of six tilapia groups was analyzed by adjoining method(NJ),which showed the six species of tilapia are divided into two main branches.One branch included GIFT strain of Oreochromis niloticus,Oreochromis niloticus,Oreochromis niloticus×O.mossambica,and Oreochromis mossambica.Another branch included Oreochromis niloticus×O.aureus and Oreochromis niloticus×O.aureus.In conclusion,six species of farmed tilapia had high genetic diversity in Hainan,and there were certain differences among the six different groups.The relationship between Oreochromis niloticus and Oreochromis niloticus×O.aureus was furthest,while GIFT strain of Oreochromis niloticus and Oreochromis niloticus was closest.