BACKGROUNDS:Glucans are complex polysaccharide components of yeast and fungal cell walls.This compounds can stimulate the fish immune system. OBJECTIVES: The present study investigated the effects of Beta glucan(Macrogard) on growth, survival and some immunological parameters of rainbow trout (10 mg) and also on the efficiency of Streptococcus vaccine. METHODS: Treatments of macrogard (1 g/kg food/day for 42 days), macrogard (macrogard 1 g/kg diet) with 15 minutes bathin vaccine, vaccine bath without macrogard and control were examined in a 42 daysperiod. RESULTS: In all treatments the fish growth (weight) showed a significant increase (p<0.05) compared to the control, while there was no significant difference among the treatments. The lyzosyme level of the blood serum showed a significant difference between control and the other treatments, the highest level was observed in the macrogaurd with vaccine treatment (2.7 µg/ml) and the lowest level was observed in the control(0.5 µg/ml). Leukocytes count also had a significant difference between the control (3.3%Nuetrophil) and other treatments (6.6% Nuetrophil) (p<0.05). The result of survival of fish challenged with Streptococcus iniae via bath route was 55%, while those for vaccine treatment, macrogard plus vaccine, macrogard every day and macrogard every 10 days interval were 75%, 86%, 60& and 55%, respectively. CONCLUSIONS: The results of this study showed that supplement of macrogard has positive effect on growth and non-specific immune responses of rainbow trout and can enhance efficacy of anti- streptococcus iniae vaccine in this fish.