The present study was designed and performed to investigate the effect of exogenous enzyme alpha amylase and cellulase as feed additive on total bacterial flora, Lactobacillus and growth of rainbow trout, (Oncorhynchus mykiss Walbaum, 1792) with The two diets 20 percent carbohydrates and 30 percent carbohydrates for 8 weeks. In this regard, 240 juveniles of rainbow trout (average weight 13±0.72 g) were distributed in eight experimental treatments containing feeding without exogenous enzyme level of 20% and 30% carbohydrate in diet respectively in treatments 1 and 5.containing feeding with exogenous enzyme alpha amylase (0/5mg) level of 20% and 30% carbohydrate in diet respectively in treatments 2 and 6.containing feeding with exogenous enzyme cellulase (0/5mg) level of 20and 30% carbohydrate in diet respectively in treatments 3 and 6.containing feeding with mix exogenous enzyme cellulase and alpha amylase (1:1) (0/5mg) level of 20% and 30% carbohydrate in diet respectively in treatments 4 and 8, (with three replicates, 24 fiberglass tanks 100L). Feed was offered three times a day to apparent satiation. At the end of the experiment, 10 fish per replicate were caught randomly for growth rate evaluation and two fish per replicate were caught randomly for Intestinal bacterial flora evaluation. the results showed body weight gain that had no significant difference with other treatments (P>0.05). Also the best of FCR was obsereved in treatments (1) and (6). The highest and lowest total bacterial flora and Lactobacillus were observed, respectively in treatments (8) and (1). Overall, the results showed that use of exogenous enzyme alpha amylase and cellulase caused improve Intestinal bacterial flora and feeding rates in the rainbow trout.