This study aimed at investigating the effect of probiotic bacillus on energy utilization and ammonia and urea excretion in Onchorhynchus mykiss larvea using five blends of probiotic bacillus via supplementation of diet for 60 days. Rainbow trout larvae (avg 46332 mg) were fed with the diet supplemented with 1×106 CFU/ml (treatment Tau-1), 1×107 CFU/ml (treatment Tau-2) and 1×108 CFU/ml (treatment Tau-3), per 100g food and their effects were compared with those of control diet containing no probiotic. Feeding varied from 5% to 8% of the body weight in breeding period, though the fishes were not fed during the excretion experiment. Results revealed that ammonia and urea excretion in experimental treatments had significantly decreased in comparison to control treatment (P<0.05).The lowest and highest amounts of ammonia and urea excretion in both two condition was observed in treatment Tau-2 and in control treatment, respectively. In addition, energy utilization in treatments was significantly (P<0.05) lower than control. In conclusion, probiotics bacilli can reduce the amount of energy utilization and ammonia and urea excretion.