Background: Lactococcus garvieae is one of the main causative agents of Streptococ-cos is/Lactococcosis in farmed fish particularly in rainbow trout causing remarkable losses each year. OBJECTIVES: To study the genetic diversity of Lactococcus garvieae strains recovered from the mortality of farmed rainbow trout in different provinces of Iran. METHODES: The Gram positive cocci were first obtained from the kidney tissues of diseased trout. The bacterial isolates were grown on blood agar and were then identified by PCR method. Their genetic diversities were then studied using RAPD. RESULTS: The recovered gram positive cocci strains were identified as L. garvieae producing a 1100bp in PCR procedure. In RAPD studies using 6 random primers (P1-P6), only primer P4 was able to produce higher number of bands (five bands). Therefore, using this primer four profile patterns consisting of 560-1330 bp in 5 bands, 56--1260bp in 5 bands, 560-1260bp in 4 bands and 560-1200bp in 5 bands were obtained. The phylogenetic tree of the RAPD product using UPMGA software included these strains in three different clusters with four different genetic groups. CONCLUSIONS: The results of this study clearly show that L. garvieae strains from the diseased rainbow trout in the north part of Iran are geneticly different from those in the west country, although there is some genetic similarity between some strains of these two regions of country.