The aim of the present study was to investigate the effect of replacing biosilage from chicken intestine with fish meal in the diet on serum indices, muscle quality and digestive system bacterial flora of Rainbow trout (Raised in two farms of Karkandeh village with well water and dam farm with river water-Sari city). For this purpose, after producing biosilage from the waste, diets containing 50 and 100% biosilage were prepared and the findings were evaluated along with the control. The results of serum indices in both farms showed an increase in total protein, IgM and lysozyme in 100% treatment, and 50% and control treatments were in the next order (p<0.05). The amount of albumin in the fishes of Karkandeh village was not significantly different between the treatments (p>0.05), but in the dam fishes, the highest amount was recorded in the 100% biosilage treatment (p<0.05). The amount of free oxygen radicals in the fishes of Karkandeh village in the control treatment was more than the two treatments containing biosilage (p<0.05), but in the dam fishes, the highest level of the mentioned index was reported in the 100% treatment (p<0.05). The results of carcass qualitative analysis showed that in both farms the amount of protein and ash in the treatment containing 50% of biosilage was higher than other treatments (p<0.05). But the amount of fat in the mentioned treatment was less than the others (p<0.05). In the study of bacterial flora of fish gastrointestinal tract, it was found that the population of aerobic and lacticacid bacteria was significantly higher in 50% biosilage treatment than the other two treatments, and 100% and control treatments were in the next rank, respectively (p<0.05). According to the findings, the use of biosilage is a desirable alternative to fish meal in the Rainbow trout diet and helps to improve serum indices, muscle quality and bacterial flora of the gastrointestinal tract.