240 rainbow trout fingerlings weighting 16 gram were randomly allocated into three treatment groups including 0.5, 1.0and 1.5 gr/kg of Echinacea purpurea extract in food, and a control group (without EPE in food), each intriplicates for 60 days. At sampling times, some of hematological and biochemical parameters including C₃ and C₄ complements, oxygen free radicals, lysozyme activity, and other hemathological parameters were analyzed. Also, at the end of the experiment,fishes challenged with Streptococcus iniae and the mortality was analyzed. However, there were no significant differences in C₄, total immunoglobulin, lymphocyte and monocyte (p>0.05). The amount of glucose, serum total protein and albumin decreased at the end of the experiment significantly (p<0.05). In addition, the results showed that mortality percentage in Echinacea treatment group with 1.5 gr/kg concentration was significantly lower than other treatment groups (p<0.05). In conclusion the results haveshown that Echinacea extract had the positive effect on immunity responses of rainbow trout especially in higher concentration (1.5gr/kg). Also, adding Echinacea extract in rainbow trout diet increased the resistance of rainbow trout against S. iniae.