BACKGROUND: Enhancement of the immune system seems to be the most promising method of preventing fish diseases and increasing growth rate. Biodegradable and biocompatible immunostimulants obtained from natural sources (particularly herbal extracts) have received great attention for fish. OBJECTIVES: In this study the immunostimulatory and growth stimulation effects of herbal extracts (Echinacea purpurea, Boswellia thurifera, Zataria multiflora), Ergosan and Levamisole were evaluated in common carp. METHODS: 450 fish (11.12±1.22 g) were randomly divided into 6 groups in triplicate and fed with experimental diet for 6 weeks. Fish in groups 1 to 5 were fed by food supplemented with E. purpurea, B.thurifera, Z.multiflora, Ergosan and Levamisole, respectively. Group 6 was fed with basal food without supplementation. The Growth performance indices were evaluated at the end of study and blood samples were collected from 6 fish in each group. packed cell volume, haemoglobin concentration, red blood cell counts, white blood cell counts mean corpuscular hemoglobin, mean corpuscular volume and mean corpuscular hemoglobin concentration were compared among the groups. In each group, thirty fish were challenged with live Aeromonas hydrophila on day 42 and mortality rate was studied. RESULTS: Mortality rate showed no significant difference among groups (p>0.05). Specific growth rate (SGR) and food conversion rate (FCR) showed significant increase in all groups except (Zataria multiflora) compared to the control. Post challenge mortality rate decreased in all groups except (Zataria multiflora) compared to the control (p<0.05). WBC values in Ergosan, E. purpurea and levamisole groups were 7830±590, 7750±500 and 7380±810 per mL respectively which, showed significant (p<0.05) increased compared to the control group (6380±123mL), However no significant changes were seen in the other haematological parameters (p>0.05). CONCLUSIONS: It can be concluded that extract of E. purpurea and B.thurifera have immunostimulatory and growth stimulation effects in common carp which are comparable with the effects of two well documented fish immunostimulants, Ergosan and Levamisole.