In this study Bacillus subtilis is used for control of streptococcosis with the agentof Streptococcus iniae in Rainbow trout. The experience was carried out in 2groups (Control and Treatment) and 3 replicates. In Control group, probiotic wasnot applied in diet but in Treatment group, Bacillus subtilis was administered infeed at a concentration of 107 cells g -1. In the day of forty five, 0.1 mlintraperitoneally injection of S.iniae with 2×107 cells ml-1 dosage was done forboth of groups and were checked for the rest of the survey duration (2 weeks). Atthe end of the time which took about two months, blood samples were caught forbiochemical experiments for realizing the effect of B.subtilis feeding on resistanceof fish against S.iniae infection. After injection of S.iniae, there was no significantdifference among Control(C) and Treatment(T) groups considering parameterssuch as glucose and aspartate aminotransferase (p>0.05). But significantdifference was seen in the serum total protein, serum albumin, IgM, lysozyme, urea, Alanin aminotransferase and alkaline phosphatase in both groups (p<0.05).The serum total protein, serum albumin, IgM and lysozyme were higher in Tgroup and urea, Alanin aminotransferase and alkaline phosphatase were lower incomparison with the control. The results of the present study indicate thatB.subtilis can be used as an agent for the control of streptococcosis in Rainbowtrout hatchery and culture farms for decreasing economical disasters.