Abstract: Using phylogenetic and cluster analysis, we studied 15 strains of bacteria isolated from eight species of South China sampling andinspected fish that were suffering from sarcoidosis. Phylogenetic analysis indicates that the 16S rDNA sequences of 15 isolated strains, which share 99% similarity to that of Nocardia seriolae, have a close evolutionary relationship with the member of the N.seriolae, and could be grouped into 2 clusers. Cluster analysis shows that 15 isolated strains could be divided into two groups when T=23, which could be divided into two and four subgroups respectively when T=11. The results suggest that diversity exists in the 15 strains of N. seriolae.